diff --git a/CHANGELOG.md b/CHANGELOG.md
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--- /dev/null
+++ b/CHANGELOG.md
@@ -0,0 +1,11 @@
+# Changelog for webgear-openapi
+
+## [Unreleased]
+
+## [1.0.0] - 2022-01-08
+
+### Added
+- First version of webgear-openapi
+
+[Unreleased]: https://github.com/haskell-webgear/webgear/compare/v1.0.0...HEAD
+[1.0.0]: https://github.com/haskell-webgear/webgear/releases/tag/v1.0.0
diff --git a/LICENSE b/LICENSE
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--- /dev/null
+++ b/LICENSE
@@ -0,0 +1,373 @@
+Mozilla Public License Version 2.0
+==================================
+
+1. Definitions
+--------------
+
+1.1. "Contributor"
+    means each individual or legal entity that creates, contributes to
+    the creation of, or owns Covered Software.
+
+1.2. "Contributor Version"
+    means the combination of the Contributions of others (if any) used
+    by a Contributor and that particular Contributor's Contribution.
+
+1.3. "Contribution"
+    means Covered Software of a particular Contributor.
+
+1.4. "Covered Software"
+    means Source Code Form to which the initial Contributor has attached
+    the notice in Exhibit A, the Executable Form of such Source Code
+    Form, and Modifications of such Source Code Form, in each case
+    including portions thereof.
+
+1.5. "Incompatible With Secondary Licenses"
+    means
+
+    (a) that the initial Contributor has attached the notice described
+        in Exhibit B to the Covered Software; or
+
+    (b) that the Covered Software was made available under the terms of
+        version 1.1 or earlier of the License, but not also under the
+        terms of a Secondary License.
+
+1.6. "Executable Form"
+    means any form of the work other than Source Code Form.
+
+1.7. "Larger Work"
+    means a work that combines Covered Software with other material, in
+    a separate file or files, that is not Covered Software.
+
+1.8. "License"
+    means this document.
+
+1.9. "Licensable"
+    means having the right to grant, to the maximum extent possible,
+    whether at the time of the initial grant or subsequently, any and
+    all of the rights conveyed by this License.
+
+1.10. "Modifications"
+    means any of the following:
+
+    (a) any file in Source Code Form that results from an addition to,
+        deletion from, or modification of the contents of Covered
+        Software; or
+
+    (b) any new file in Source Code Form that contains any Covered
+        Software.
+
+1.11. "Patent Claims" of a Contributor
+    means any patent claim(s), including without limitation, method,
+    process, and apparatus claims, in any patent Licensable by such
+    Contributor that would be infringed, but for the grant of the
+    License, by the making, using, selling, offering for sale, having
+    made, import, or transfer of either its Contributions or its
+    Contributor Version.
+
+1.12. "Secondary License"
+    means either the GNU General Public License, Version 2.0, the GNU
+    Lesser General Public License, Version 2.1, the GNU Affero General
+    Public License, Version 3.0, or any later versions of those
+    licenses.
+
+1.13. "Source Code Form"
+    means the form of the work preferred for making modifications.
+
+1.14. "You" (or "Your")
+    means an individual or a legal entity exercising rights under this
+    License. For legal entities, "You" includes any entity that
+    controls, is controlled by, or is under common control with You. For
+    purposes of this definition, "control" means (a) the power, direct
+    or indirect, to cause the direction or management of such entity,
+    whether by contract or otherwise, or (b) ownership of more than
+    fifty percent (50%) of the outstanding shares or beneficial
+    ownership of such entity.
+
+2. License Grants and Conditions
+--------------------------------
+
+2.1. Grants
+
+Each Contributor hereby grants You a world-wide, royalty-free,
+non-exclusive license:
+
+(a) under intellectual property rights (other than patent or trademark)
+    Licensable by such Contributor to use, reproduce, make available,
+    modify, display, perform, distribute, and otherwise exploit its
+    Contributions, either on an unmodified basis, with Modifications, or
+    as part of a Larger Work; and
+
+(b) under Patent Claims of such Contributor to make, use, sell, offer
+    for sale, have made, import, and otherwise transfer either its
+    Contributions or its Contributor Version.
+
+2.2. Effective Date
+
+The licenses granted in Section 2.1 with respect to any Contribution
+become effective for each Contribution on the date the Contributor first
+distributes such Contribution.
+
+2.3. Limitations on Grant Scope
+
+The licenses granted in this Section 2 are the only rights granted under
+this License. No additional rights or licenses will be implied from the
+distribution or licensing of Covered Software under this License.
+Notwithstanding Section 2.1(b) above, no patent license is granted by a
+Contributor:
+
+(a) for any code that a Contributor has removed from Covered Software;
+    or
+
+(b) for infringements caused by: (i) Your and any other third party's
+    modifications of Covered Software, or (ii) the combination of its
+    Contributions with other software (except as part of its Contributor
+    Version); or
+
+(c) under Patent Claims infringed by Covered Software in the absence of
+    its Contributions.
+
+This License does not grant any rights in the trademarks, service marks,
+or logos of any Contributor (except as may be necessary to comply with
+the notice requirements in Section 3.4).
+
+2.4. Subsequent Licenses
+
+No Contributor makes additional grants as a result of Your choice to
+distribute the Covered Software under a subsequent version of this
+License (see Section 10.2) or under the terms of a Secondary License (if
+permitted under the terms of Section 3.3).
+
+2.5. Representation
+
+Each Contributor represents that the Contributor believes its
+Contributions are its original creation(s) or it has sufficient rights
+to grant the rights to its Contributions conveyed by this License.
+
+2.6. Fair Use
+
+This License is not intended to limit any rights You have under
+applicable copyright doctrines of fair use, fair dealing, or other
+equivalents.
+
+2.7. Conditions
+
+Sections 3.1, 3.2, 3.3, and 3.4 are conditions of the licenses granted
+in Section 2.1.
+
+3. Responsibilities
+-------------------
+
+3.1. Distribution of Source Form
+
+All distribution of Covered Software in Source Code Form, including any
+Modifications that You create or to which You contribute, must be under
+the terms of this License. You must inform recipients that the Source
+Code Form of the Covered Software is governed by the terms of this
+License, and how they can obtain a copy of this License. You may not
+attempt to alter or restrict the recipients' rights in the Source Code
+Form.
+
+3.2. Distribution of Executable Form
+
+If You distribute Covered Software in Executable Form then:
+
+(a) such Covered Software must also be made available in Source Code
+    Form, as described in Section 3.1, and You must inform recipients of
+    the Executable Form how they can obtain a copy of such Source Code
+    Form by reasonable means in a timely manner, at a charge no more
+    than the cost of distribution to the recipient; and
+
+(b) You may distribute such Executable Form under the terms of this
+    License, or sublicense it under different terms, provided that the
+    license for the Executable Form does not attempt to limit or alter
+    the recipients' rights in the Source Code Form under this License.
+
+3.3. Distribution of a Larger Work
+
+You may create and distribute a Larger Work under terms of Your choice,
+provided that You also comply with the requirements of this License for
+the Covered Software. If the Larger Work is a combination of Covered
+Software with a work governed by one or more Secondary Licenses, and the
+Covered Software is not Incompatible With Secondary Licenses, this
+License permits You to additionally distribute such Covered Software
+under the terms of such Secondary License(s), so that the recipient of
+the Larger Work may, at their option, further distribute the Covered
+Software under the terms of either this License or such Secondary
+License(s).
+
+3.4. Notices
+
+You may not remove or alter the substance of any license notices
+(including copyright notices, patent notices, disclaimers of warranty,
+or limitations of liability) contained within the Source Code Form of
+the Covered Software, except that You may alter any license notices to
+the extent required to remedy known factual inaccuracies.
+
+3.5. Application of Additional Terms
+
+You may choose to offer, and to charge a fee for, warranty, support,
+indemnity or liability obligations to one or more recipients of Covered
+Software. However, You may do so only on Your own behalf, and not on
+behalf of any Contributor. You must make it absolutely clear that any
+such warranty, support, indemnity, or liability obligation is offered by
+You alone, and You hereby agree to indemnify every Contributor for any
+liability incurred by such Contributor as a result of warranty, support,
+indemnity or liability terms You offer. You may include additional
+disclaimers of warranty and limitations of liability specific to any
+jurisdiction.
+
+4. Inability to Comply Due to Statute or Regulation
+---------------------------------------------------
+
+If it is impossible for You to comply with any of the terms of this
+License with respect to some or all of the Covered Software due to
+statute, judicial order, or regulation then You must: (a) comply with
+the terms of this License to the maximum extent possible; and (b)
+describe the limitations and the code they affect. Such description must
+be placed in a text file included with all distributions of the Covered
+Software under this License. Except to the extent prohibited by statute
+or regulation, such description must be sufficiently detailed for a
+recipient of ordinary skill to be able to understand it.
+
+5. Termination
+--------------
+
+5.1. The rights granted under this License will terminate automatically
+if You fail to comply with any of its terms. However, if You become
+compliant, then the rights granted under this License from a particular
+Contributor are reinstated (a) provisionally, unless and until such
+Contributor explicitly and finally terminates Your grants, and (b) on an
+ongoing basis, if such Contributor fails to notify You of the
+non-compliance by some reasonable means prior to 60 days after You have
+come back into compliance. Moreover, Your grants from a particular
+Contributor are reinstated on an ongoing basis if such Contributor
+notifies You of the non-compliance by some reasonable means, this is the
+first time You have received notice of non-compliance with this License
+from such Contributor, and You become compliant prior to 30 days after
+Your receipt of the notice.
+
+5.2. If You initiate litigation against any entity by asserting a patent
+infringement claim (excluding declaratory judgment actions,
+counter-claims, and cross-claims) alleging that a Contributor Version
+directly or indirectly infringes any patent, then the rights granted to
+You by any and all Contributors for the Covered Software under Section
+2.1 of this License shall terminate.
+
+5.3. In the event of termination under Sections 5.1 or 5.2 above, all
+end user license agreements (excluding distributors and resellers) which
+have been validly granted by You or Your distributors under this License
+prior to termination shall survive termination.
+
+************************************************************************
+*                                                                      *
+*  6. Disclaimer of Warranty                                           *
+*  -------------------------                                           *
+*                                                                      *
+*  Covered Software is provided under this License on an "as is"       *
+*  basis, without warranty of any kind, either expressed, implied, or  *
+*  statutory, including, without limitation, warranties that the       *
+*  Covered Software is free of defects, merchantable, fit for a        *
+*  particular purpose or non-infringing. The entire risk as to the     *
+*  quality and performance of the Covered Software is with You.        *
+*  Should any Covered Software prove defective in any respect, You     *
+*  (not any Contributor) assume the cost of any necessary servicing,   *
+*  repair, or correction. This disclaimer of warranty constitutes an   *
+*  essential part of this License. No use of any Covered Software is   *
+*  authorized under this License except under this disclaimer.         *
+*                                                                      *
+************************************************************************
+
+************************************************************************
+*                                                                      *
+*  7. Limitation of Liability                                          *
+*  --------------------------                                          *
+*                                                                      *
+*  Under no circumstances and under no legal theory, whether tort      *
+*  (including negligence), contract, or otherwise, shall any           *
+*  Contributor, or anyone who distributes Covered Software as          *
+*  permitted above, be liable to You for any direct, indirect,         *
+*  special, incidental, or consequential damages of any character      *
+*  including, without limitation, damages for lost profits, loss of    *
+*  goodwill, work stoppage, computer failure or malfunction, or any    *
+*  and all other commercial damages or losses, even if such party      *
+*  shall have been informed of the possibility of such damages. This   *
+*  limitation of liability shall not apply to liability for death or   *
+*  personal injury resulting from such party's negligence to the       *
+*  extent applicable law prohibits such limitation. Some               *
+*  jurisdictions do not allow the exclusion or limitation of           *
+*  incidental or consequential damages, so this exclusion and          *
+*  limitation may not apply to You.                                    *
+*                                                                      *
+************************************************************************
+
+8. Litigation
+-------------
+
+Any litigation relating to this License may be brought only in the
+courts of a jurisdiction where the defendant maintains its principal
+place of business and such litigation shall be governed by laws of that
+jurisdiction, without reference to its conflict-of-law provisions.
+Nothing in this Section shall prevent a party's ability to bring
+cross-claims or counter-claims.
+
+9. Miscellaneous
+----------------
+
+This License represents the complete agreement concerning the subject
+matter hereof. If any provision of this License is held to be
+unenforceable, such provision shall be reformed only to the extent
+necessary to make it enforceable. Any law or regulation which provides
+that the language of a contract shall be construed against the drafter
+shall not be used to construe this License against a Contributor.
+
+10. Versions of the License
+---------------------------
+
+10.1. New Versions
+
+Mozilla Foundation is the license steward. Except as provided in Section
+10.3, no one other than the license steward has the right to modify or
+publish new versions of this License. Each version will be given a
+distinguishing version number.
+
+10.2. Effect of New Versions
+
+You may distribute the Covered Software under the terms of the version
+of the License under which You originally received the Covered Software,
+or under the terms of any subsequent version published by the license
+steward.
+
+10.3. Modified Versions
+
+If you create software not governed by this License, and you want to
+create a new license for such software, you may create and use a
+modified version of this License if you rename the license and remove
+any references to the name of the license steward (except to note that
+such modified license differs from this License).
+
+10.4. Distributing Source Code Form that is Incompatible With Secondary
+Licenses
+
+If You choose to distribute Source Code Form that is Incompatible With
+Secondary Licenses under the terms of this version of the License, the
+notice described in Exhibit B of this License must be attached.
+
+Exhibit A - Source Code Form License Notice
+-------------------------------------------
+
+  This Source Code Form is subject to the terms of the Mozilla Public
+  License, v. 2.0. If a copy of the MPL was not distributed with this
+  file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+If it is not possible or desirable to put the notice in a particular
+file, then You may include the notice in a location (such as a LICENSE
+file in a relevant directory) where a recipient would be likely to look
+for such a notice.
+
+You may add additional accurate notices of copyright ownership.
+
+Exhibit B - "Incompatible With Secondary Licenses" Notice
+---------------------------------------------------------
+
+  This Source Code Form is "Incompatible With Secondary Licenses", as
+  defined by the Mozilla Public License, v. 2.0.
diff --git a/README.md b/README.md
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--- /dev/null
+++ b/README.md
@@ -0,0 +1,6 @@
+# WebGear - HTTP API server
+
+[![Hackage](https://img.shields.io/hackage/v/webgear-openapi)](https://hackage.haskell.org/package/webgear-openapi)
+
+WebGear is a Haskell library for building composable, type-safe HTTP APIs. This package helps to generate OpenAPI
+specifications from WebGear API specifications.
diff --git a/src/WebGear/OpenApi.hs b/src/WebGear/OpenApi.hs
new file mode 100644
--- /dev/null
+++ b/src/WebGear/OpenApi.hs
@@ -0,0 +1,27 @@
+{- | Main module for WebGear OpenAPI support.
+
+ Import this module to get all required types and functions for
+ generating OpenAPI documentation. Alternatively, import individual
+ modules under @WebGear.OpenApi@.
+
+ Typical usage to generate OpenAPI:
+
+@
+ import WebGear.OpenApi
+ import Data.OpenApi (OpenApi)
+
+ myHandler :: Handler h m => RequestHandler h '[]
+ myHandler = ....
+
+ documentation :: OpenApi
+ documentation = toOpenApi myHandler
+@
+-}
+module WebGear.OpenApi (
+  module WebGear.Core,
+  module WebGear.OpenApi.Handler,
+) where
+
+import WebGear.Core
+import WebGear.OpenApi.Handler
+import WebGear.OpenApi.Traits ()
diff --git a/src/WebGear/OpenApi/Handler.hs b/src/WebGear/OpenApi/Handler.hs
new file mode 100644
--- /dev/null
+++ b/src/WebGear/OpenApi/Handler.hs
@@ -0,0 +1,339 @@
+{- | An implementation of `Handler` to generate `OpenApi` documentation
+ from WebGear API specifications.
+-}
+module WebGear.OpenApi.Handler (
+  OpenApiHandler (..),
+  DocNode (..),
+  Tree,
+  singletonNode,
+  nullNode,
+  toOpenApi,
+) where
+
+import Control.Applicative ((<|>))
+import Control.Arrow (Arrow (..), ArrowChoice (..), ArrowPlus (..), ArrowZero (..))
+import Control.Arrow.Operations (ArrowError (..))
+import qualified Control.Category as Cat
+import Control.Lens (at, (%~), (&), (.~), (<>~), (?~))
+import qualified Data.HashMap.Strict.InsOrd as Map
+import Data.OpenApi
+import Data.OpenApi.Internal.Utils (swaggerMappend)
+import Data.Text (Text)
+import qualified Data.Text as Text
+import Network.HTTP.Media.MediaType (MediaType)
+import qualified Network.HTTP.Types as HTTP
+import WebGear.Core.Handler (Description (..), Handler (..), RouteMismatch, RoutePath (..), Summary (..))
+
+-- | A tree where internal nodes have one or two children.
+data Tree a
+  = NullNode
+  | SingleNode a (Tree a)
+  | BinaryNode (Tree a) (Tree a)
+  deriving stock (Show)
+
+-- | Different types of documentation elements captured by the handler
+data DocNode
+  = DocSecurityScheme Text SecurityScheme
+  | DocRequestBody (Definitions Schema) RequestBody
+  | DocResponseBody (Definitions Schema) MediaType MediaTypeObject
+  | DocRequestHeader Param
+  | DocResponseHeader HeaderName Header
+  | DocMethod HTTP.StdMethod
+  | DocPathElem Text
+  | DocPathVar Param
+  | DocQueryParam Param
+  | DocStatus HTTP.Status
+  | DocSummary Summary
+  | DocDescription Description
+  deriving stock (Show)
+
+-- | Documentation elements after compaction
+data CompactDocNode
+  = CDocSecurityScheme Text SecurityScheme
+  | CDocRequestBody (Definitions Schema) RequestBody
+  | CDocResponseBody (Definitions Schema) MediaType MediaTypeObject
+  | CDocRequestHeader Param
+  | CDocResponseHeader HeaderName Header
+  | CDocMethod HTTP.StdMethod
+  | CDocPathElem Text
+  | CDocPathVar Param
+  | CDocRouteDoc (Maybe Summary) (Maybe Description)
+  | CDocQueryParam Param
+  | CDocStatus HTTP.Status (Maybe Description)
+  deriving stock (Show)
+
+-- | Generate a tree with a single node
+singletonNode :: a -> Tree a
+singletonNode a = SingleNode a NullNode
+
+-- | Generate an empty tree
+nullNode :: Tree a
+nullNode = NullNode
+
+{- | A handler that captured `OpenApi` documentation of API
+ specifications.
+-}
+newtype OpenApiHandler m a b = OpenApiHandler
+  {openApiDoc :: Tree DocNode}
+
+instance Cat.Category (OpenApiHandler m) where
+  id :: OpenApiHandler m a a
+  id = OpenApiHandler{openApiDoc = NullNode}
+
+  (.) :: OpenApiHandler m b c -> OpenApiHandler m a b -> OpenApiHandler m a c
+  OpenApiHandler doc2 . OpenApiHandler doc1 = OpenApiHandler $ insertAsLeaf doc1 doc2
+    where
+      insertAsLeaf :: Tree DocNode -> Tree DocNode -> Tree DocNode
+      insertAsLeaf parent child = case parent of
+        NullNode -> child
+        SingleNode doc next -> SingleNode doc (insertAsLeaf next child)
+        BinaryNode b1 b2 -> BinaryNode (insertAsLeaf b1 child) (insertAsLeaf b2 child)
+
+instance Arrow (OpenApiHandler m) where
+  arr :: (a -> b) -> OpenApiHandler m a b
+  arr _ = OpenApiHandler{openApiDoc = NullNode}
+
+  first :: OpenApiHandler m b c -> OpenApiHandler m (b, d) (c, d)
+  first (OpenApiHandler doc) = OpenApiHandler doc
+
+  second :: OpenApiHandler m b c -> OpenApiHandler m (d, b) (d, c)
+  second (OpenApiHandler doc) = OpenApiHandler doc
+
+instance ArrowZero (OpenApiHandler m) where
+  zeroArrow :: OpenApiHandler m b c
+  zeroArrow = OpenApiHandler{openApiDoc = NullNode}
+
+instance ArrowPlus (OpenApiHandler m) where
+  (<+>) :: OpenApiHandler m b c -> OpenApiHandler m b c -> OpenApiHandler m b c
+  OpenApiHandler NullNode <+> OpenApiHandler doc = OpenApiHandler doc
+  OpenApiHandler doc <+> OpenApiHandler NullNode = OpenApiHandler doc
+  OpenApiHandler doc1 <+> OpenApiHandler doc2 = OpenApiHandler $ BinaryNode doc1 doc2
+
+instance ArrowChoice (OpenApiHandler m) where
+  left :: OpenApiHandler m b c -> OpenApiHandler m (Either b d) (Either c d)
+  left (OpenApiHandler doc) = OpenApiHandler doc
+
+  right :: OpenApiHandler m b c -> OpenApiHandler m (Either d b) (Either d c)
+  right (OpenApiHandler doc) = OpenApiHandler doc
+
+  (+++) :: OpenApiHandler m b c -> OpenApiHandler m b' c' -> OpenApiHandler m (Either b b') (Either c c')
+  OpenApiHandler doc +++ OpenApiHandler NullNode = OpenApiHandler doc
+  OpenApiHandler NullNode +++ OpenApiHandler doc = OpenApiHandler doc
+  OpenApiHandler doc1 +++ OpenApiHandler doc2 = OpenApiHandler $ BinaryNode doc1 doc2
+
+  (|||) :: OpenApiHandler m b d -> OpenApiHandler m c d -> OpenApiHandler m (Either b c) d
+  OpenApiHandler doc ||| OpenApiHandler NullNode = OpenApiHandler doc
+  OpenApiHandler NullNode ||| OpenApiHandler doc = OpenApiHandler doc
+  OpenApiHandler doc1 ||| OpenApiHandler doc2 = OpenApiHandler $ BinaryNode doc1 doc2
+
+instance ArrowError RouteMismatch (OpenApiHandler m) where
+  {-# INLINEABLE raise #-}
+  raise = OpenApiHandler{openApiDoc = NullNode}
+
+  {-# INLINEABLE handle #-}
+  OpenApiHandler doc1 `handle` OpenApiHandler doc2 = OpenApiHandler $ BinaryNode doc1 doc2
+
+  {-# INLINEABLE tryInUnless #-}
+  tryInUnless (OpenApiHandler doc1) (OpenApiHandler doc2) (OpenApiHandler doc3) =
+    OpenApiHandler $ BinaryNode (BinaryNode doc1 doc2) doc3
+
+instance Monad m => Handler (OpenApiHandler m) m where
+  {-# INLINEABLE arrM #-}
+  arrM :: (a -> m b) -> OpenApiHandler m a b
+  arrM _ = OpenApiHandler{openApiDoc = NullNode}
+
+  {-# INLINEABLE consumeRoute #-}
+  consumeRoute :: OpenApiHandler m RoutePath a -> OpenApiHandler m () a
+  consumeRoute (OpenApiHandler doc) = OpenApiHandler doc
+
+  {-# INLINEABLE setDescription #-}
+  setDescription :: Description -> OpenApiHandler m a a
+  setDescription = OpenApiHandler . singletonNode . DocDescription
+
+  {-# INLINEABLE setSummary #-}
+  setSummary :: Summary -> OpenApiHandler m a a
+  setSummary = OpenApiHandler . singletonNode . DocSummary
+
+-- | Generate OpenApi documentation from a handler
+toOpenApi :: OpenApiHandler m a b -> OpenApi
+toOpenApi = go . compact . openApiDoc
+  where
+    go t = case t of
+      NullNode -> mempty
+      SingleNode parent child -> mergeDoc parent child mempty
+      BinaryNode t1 t2 -> go t1 `combineOpenApi` go t2
+
+compact :: Tree DocNode -> Tree CompactDocNode
+compact t = let (_, _, t') = go t in t'
+  where
+    go = \case
+      NullNode -> (Nothing, Nothing, NullNode)
+      BinaryNode t1 t2 ->
+        let (descr1, summ1, t1') = go t1
+            (descr2, summ2, t2') = go t2
+         in (descr1 <|> descr2, summ1 <|> summ2, BinaryNode t1' t2')
+      SingleNode node child -> compactDoc node child
+
+    compactDoc :: DocNode -> Tree DocNode -> (Maybe Description, Maybe Summary, Tree CompactDocNode)
+    compactDoc (DocSecurityScheme schemeName scheme) child =
+      let (descr, summ, child') = go child
+          scheme' = scheme & description .~ fmap getDescription descr
+       in (Nothing, summ, SingleNode (CDocSecurityScheme schemeName scheme') child')
+    compactDoc (DocRequestBody defs body) child =
+      let (descr, summ, child') = go child
+          body' = body & description .~ fmap getDescription descr
+       in (Nothing, summ, SingleNode (CDocRequestBody defs body') child')
+    compactDoc (DocResponseBody defs mediaType mediaTypeObject) child =
+      SingleNode (CDocResponseBody defs mediaType mediaTypeObject) <$> go child
+    compactDoc (DocRequestHeader param) child =
+      let (descr, summ, child') = go child
+          param' = param & description .~ fmap getDescription descr
+       in (Nothing, summ, SingleNode (CDocRequestHeader param') child')
+    compactDoc (DocResponseHeader headerName header) child =
+      let (descr, summ, child') = go child
+          header' = header & description .~ fmap getDescription descr
+       in (Nothing, summ, SingleNode (CDocResponseHeader headerName header') child')
+    compactDoc (DocMethod m) child =
+      (Nothing, Nothing, addRouteDoc (CDocMethod m) child)
+    compactDoc (DocPathElem path) child =
+      (Nothing, Nothing, addRouteDoc (CDocPathElem path) child)
+    compactDoc (DocPathVar param) child =
+      (Nothing, Nothing, addRouteDoc (CDocPathVar param) child)
+    compactDoc (DocQueryParam param) child =
+      let (descr, summ, child') = go child
+          param' = param & description .~ fmap getDescription descr
+       in (Nothing, summ, SingleNode (CDocQueryParam param') child')
+    compactDoc (DocStatus status) child =
+      let (descr, summ, child') = go child
+       in (Nothing, summ, SingleNode (CDocStatus status descr) child')
+    compactDoc (DocSummary summ) child =
+      let (descr, _, child') = go child
+       in (descr, Just summ, child')
+    compactDoc (DocDescription descr) child =
+      let (_, summ, child') = go child
+       in (Just descr, summ, child')
+
+    addRouteDoc :: CompactDocNode -> Tree DocNode -> Tree CompactDocNode
+    addRouteDoc node child = case go child of
+      (Nothing, Nothing, child') -> SingleNode node child'
+      (descr, summ, child') -> SingleNode (CDocRouteDoc summ descr) (SingleNode node child')
+
+postOrder :: Tree CompactDocNode -> OpenApi -> (OpenApi -> OpenApi) -> OpenApi
+postOrder NullNode doc f = f doc
+postOrder (SingleNode node child) doc f = f $ mergeDoc node child doc
+postOrder (BinaryNode t1 t2) doc f =
+  f $ postOrder t1 doc id `combineOpenApi` postOrder t2 doc id
+
+preOrder :: Tree CompactDocNode -> OpenApi -> (OpenApi -> OpenApi) -> OpenApi
+preOrder NullNode doc f = f doc
+preOrder (SingleNode node child) doc f = mergeDoc node child (f doc)
+preOrder (BinaryNode t1 t2) doc f =
+  let doc' = f doc
+   in postOrder t1 doc' id `combineOpenApi` postOrder t2 doc' id
+
+combinePathItem :: PathItem -> PathItem -> PathItem
+combinePathItem s t =
+  PathItem
+    { _pathItemGet = _pathItemGet s <> _pathItemGet t
+    , _pathItemPut = _pathItemPut s <> _pathItemPut t
+    , _pathItemPost = _pathItemPost s <> _pathItemPost t
+    , _pathItemDelete = _pathItemDelete s <> _pathItemDelete t
+    , _pathItemOptions = _pathItemOptions s <> _pathItemOptions t
+    , _pathItemHead = _pathItemHead s <> _pathItemHead t
+    , _pathItemPatch = _pathItemPatch s <> _pathItemPatch t
+    , _pathItemTrace = _pathItemTrace s <> _pathItemTrace t
+    , _pathItemParameters = _pathItemParameters s <> _pathItemParameters t
+    , _pathItemSummary = _pathItemSummary s <|> _pathItemSummary t
+    , _pathItemDescription = _pathItemDescription s <|> _pathItemDescription t
+    , _pathItemServers = _pathItemServers s <> _pathItemServers t
+    }
+
+combineOpenApi :: OpenApi -> OpenApi -> OpenApi
+combineOpenApi s t =
+  OpenApi
+    { _openApiInfo = _openApiInfo s <> _openApiInfo t
+    , _openApiServers = _openApiServers s <> _openApiServers t
+    , _openApiPaths = Map.unionWith combinePathItem (_openApiPaths s) (_openApiPaths t)
+    , _openApiComponents = _openApiComponents s <> _openApiComponents t
+    , _openApiSecurity = _openApiSecurity s <> _openApiSecurity t
+    , _openApiTags = _openApiTags s <> _openApiTags t
+    , _openApiExternalDocs = _openApiExternalDocs s <|> _openApiExternalDocs t
+    }
+
+mergeDoc :: CompactDocNode -> Tree CompactDocNode -> OpenApi -> OpenApi
+mergeDoc (CDocSecurityScheme schemeName scheme) child doc =
+  let secSchemes = [(schemeName, scheme)] :: Definitions SecurityScheme
+      secReqs = [SecurityRequirement [(schemeName, [])]] :: [SecurityRequirement]
+   in postOrder child doc $ \doc' ->
+        doc'
+          & components . securitySchemes <>~ secSchemes
+          & allOperations . security <>~ secReqs
+mergeDoc (CDocRequestBody defs body) child doc =
+  postOrder child doc $ \doc' ->
+    doc'
+      & allOperations . requestBody ?~ Inline body
+      & components . schemas %~ (<> defs)
+mergeDoc (CDocRequestHeader param) child doc =
+  postOrder child doc $ \doc' ->
+    doc' & allOperations . parameters <>~ [Inline param]
+mergeDoc (CDocMethod m) child doc =
+  postOrder child doc $ \doc' ->
+    doc' & paths %~ Map.map (removeOtherMethods m)
+mergeDoc (CDocPathElem path) child doc =
+  postOrder child doc $ prependPath (Text.unpack path)
+mergeDoc (CDocPathVar param) child doc =
+  postOrder child doc $ \doc' ->
+    prependPath ("{" <> Text.unpack (_paramName param) <> "}") doc'
+      & allOperations . parameters <>~ [Inline param]
+mergeDoc (CDocRouteDoc summ descr) child doc =
+  postOrder child doc $ \doc' ->
+    doc'
+      -- keep any existing documentation
+      & allOperations . summary %~ (<|> fmap getSummary summ)
+      & allOperations . description %~ (<|> fmap getDescription descr)
+mergeDoc (CDocQueryParam param) child doc =
+  postOrder child doc $ \doc' ->
+    doc' & allOperations . parameters <>~ [Inline param]
+mergeDoc (CDocStatus status descr) child doc =
+  preOrder child doc $ \doc' ->
+    let resp =
+          mempty @Response
+            & description .~ maybe "" getDescription descr
+        opr =
+          mempty @Operation
+            & at (HTTP.statusCode status) ?~ Inline resp
+        pathItem =
+          mempty @PathItem
+            & get ?~ opr
+            & put ?~ opr
+            & post ?~ opr
+            & delete ?~ opr
+            & options ?~ opr
+            & head_ ?~ opr
+            & patch ?~ opr
+            & trace ?~ opr
+     in doc' & paths <>~ [("/", pathItem)]
+mergeDoc (CDocResponseBody defs mediaType mediaTypeObject) child doc =
+  postOrder child doc $ \doc' ->
+    let resp = mempty @Response & content <>~ [(mediaType, mediaTypeObject)]
+     in doc'
+          & allOperations . responses . responses %~ Map.map (`swaggerMappend` Inline resp)
+          & components . schemas %~ (<> defs)
+mergeDoc (CDocResponseHeader headerName header) child doc =
+  postOrder child doc $ \doc' ->
+    let resp = mempty @Response & headers <>~ [(headerName, Inline header)]
+     in doc' & allOperations . responses . responses %~ Map.map (`swaggerMappend` Inline resp)
+
+removeOtherMethods :: HTTP.StdMethod -> PathItem -> PathItem
+removeOtherMethods method PathItem{..} =
+  case method of
+    HTTP.GET -> mempty{_pathItemGet, _pathItemSummary, _pathItemDescription, _pathItemServers, _pathItemParameters}
+    HTTP.PUT -> mempty{_pathItemPut, _pathItemSummary, _pathItemDescription, _pathItemServers, _pathItemParameters}
+    HTTP.POST -> mempty{_pathItemPost, _pathItemSummary, _pathItemDescription, _pathItemServers, _pathItemParameters}
+    HTTP.DELETE -> mempty{_pathItemDelete, _pathItemSummary, _pathItemDescription, _pathItemServers, _pathItemParameters}
+    HTTP.HEAD -> mempty{_pathItemHead, _pathItemSummary, _pathItemDescription, _pathItemServers, _pathItemParameters}
+    HTTP.TRACE -> mempty{_pathItemTrace, _pathItemSummary, _pathItemDescription, _pathItemServers, _pathItemParameters}
+    HTTP.OPTIONS -> mempty{_pathItemOptions, _pathItemSummary, _pathItemDescription, _pathItemServers, _pathItemParameters}
+    HTTP.PATCH -> mempty{_pathItemPatch, _pathItemSummary, _pathItemDescription, _pathItemServers, _pathItemParameters}
+    -- OpenApi does not support CONNECT
+    HTTP.CONNECT -> mempty{_pathItemSummary, _pathItemDescription, _pathItemServers, _pathItemParameters}
diff --git a/src/WebGear/OpenApi/Trait/Auth/Basic.hs b/src/WebGear/OpenApi/Trait/Auth/Basic.hs
new file mode 100644
--- /dev/null
+++ b/src/WebGear/OpenApi/Trait/Auth/Basic.hs
@@ -0,0 +1,27 @@
+{-# OPTIONS_GHC -Wno-orphans #-}
+
+-- | OpenApi implementation of 'BasicAuth'' trait.
+module WebGear.OpenApi.Trait.Auth.Basic where
+
+import Data.OpenApi
+import Data.Proxy (Proxy (..))
+import Data.String (fromString)
+import GHC.TypeLits (KnownSymbol, symbolVal)
+import WebGear.Core.Request (Request)
+import WebGear.Core.Trait (Attribute, Get (..), Linked, TraitAbsence (Absence))
+import WebGear.Core.Trait.Auth.Basic (BasicAuth' (..))
+import WebGear.OpenApi.Handler (DocNode (DocSecurityScheme), OpenApiHandler (..), singletonNode)
+
+instance (TraitAbsence (BasicAuth' x scheme m e a) Request, KnownSymbol scheme) => Get (OpenApiHandler m) (BasicAuth' x scheme m e a) Request where
+  {-# INLINEABLE getTrait #-}
+  getTrait ::
+    BasicAuth' x scheme m e a ->
+    OpenApiHandler m (Linked ts Request) (Either (Absence (BasicAuth' x scheme m e a) Request) (Attribute (BasicAuth' x scheme m e a) Request))
+  getTrait _ =
+    let schemeName = "http" <> fromString (symbolVal (Proxy @scheme))
+        securityScheme =
+          SecurityScheme
+            { _securitySchemeType = SecuritySchemeHttp HttpSchemeBasic
+            , _securitySchemeDescription = Nothing
+            }
+     in OpenApiHandler $ singletonNode (DocSecurityScheme schemeName securityScheme)
diff --git a/src/WebGear/OpenApi/Trait/Auth/JWT.hs b/src/WebGear/OpenApi/Trait/Auth/JWT.hs
new file mode 100644
--- /dev/null
+++ b/src/WebGear/OpenApi/Trait/Auth/JWT.hs
@@ -0,0 +1,30 @@
+{-# OPTIONS_GHC -Wno-orphans #-}
+
+-- | OpenApi implementation of 'JWTAuth'' trait.
+module WebGear.OpenApi.Trait.Auth.JWT where
+
+import Data.OpenApi
+import Data.String (fromString)
+import Data.Typeable (Proxy (..))
+import GHC.TypeLits (KnownSymbol, symbolVal)
+import WebGear.Core.Request (Request)
+import WebGear.Core.Trait (Attribute, Get (..), Linked, TraitAbsence (..))
+import WebGear.Core.Trait.Auth.JWT (JWTAuth' (..))
+import WebGear.OpenApi.Handler (DocNode (DocSecurityScheme), OpenApiHandler (..), singletonNode)
+
+instance
+  (TraitAbsence (JWTAuth' x scheme m e a) Request, KnownSymbol scheme) =>
+  Get (OpenApiHandler m) (JWTAuth' x scheme m e a) Request
+  where
+  {-# INLINEABLE getTrait #-}
+  getTrait ::
+    JWTAuth' x scheme m e a ->
+    OpenApiHandler m (Linked ts Request) (Either (Absence (JWTAuth' x scheme m e a) Request) (Attribute (JWTAuth' x scheme m e a) Request))
+  getTrait _ =
+    let schemeName = "http" <> fromString (symbolVal (Proxy @scheme))
+        securityScheme =
+          SecurityScheme
+            { _securitySchemeType = SecuritySchemeHttp (HttpSchemeBearer (Just "JWT"))
+            , _securitySchemeDescription = Nothing
+            }
+     in OpenApiHandler $ singletonNode (DocSecurityScheme schemeName securityScheme)
diff --git a/src/WebGear/OpenApi/Trait/Body.hs b/src/WebGear/OpenApi/Trait/Body.hs
new file mode 100644
--- /dev/null
+++ b/src/WebGear/OpenApi/Trait/Body.hs
@@ -0,0 +1,60 @@
+{-# OPTIONS_GHC -Wno-orphans #-}
+
+-- | OpenApi implementation of 'Body' trait.
+module WebGear.OpenApi.Trait.Body where
+
+import Control.Lens ((&), (.~), (?~))
+import Data.Maybe (fromMaybe)
+import Data.OpenApi hiding (Response)
+import Data.OpenApi.Declare (runDeclare)
+import Data.Proxy (Proxy (..))
+import Data.Text (Text)
+import WebGear.Core.Request (Request)
+import WebGear.Core.Response (Response (..))
+import WebGear.Core.Trait (Get (..), Linked, Set (..))
+import WebGear.Core.Trait.Body (Body (..), JSONBody (..))
+import WebGear.OpenApi.Handler (
+  DocNode (DocRequestBody, DocResponseBody),
+  OpenApiHandler (..),
+  singletonNode,
+ )
+
+instance ToSchema val => Get (OpenApiHandler m) (Body val) Request where
+  {-# INLINEABLE getTrait #-}
+  getTrait :: Body val -> OpenApiHandler m (Linked ts Request) (Either Text val)
+  getTrait (Body maybeMediaType) =
+    let mediaType = fromMaybe "*/*" maybeMediaType
+        (defs, ref) = runDeclare (declareSchemaRef $ Proxy @val) mempty
+        body =
+          (mempty @RequestBody)
+            & content .~ [(mediaType, mempty @MediaTypeObject & schema ?~ ref)]
+     in OpenApiHandler $ singletonNode (DocRequestBody defs body)
+
+instance ToSchema val => Set (OpenApiHandler m) (Body val) Response where
+  {-# INLINEABLE setTrait #-}
+  setTrait ::
+    Body val ->
+    (Linked ts Response -> Response -> val -> Linked (Body val : ts) Response) ->
+    OpenApiHandler m (Linked ts Response, val) (Linked (Body val : ts) Response)
+  setTrait (Body maybeMediaType) _ =
+    let mediaType = fromMaybe "*/*" maybeMediaType
+        (defs, ref) = runDeclare (declareSchemaRef $ Proxy @val) mempty
+        body = mempty @MediaTypeObject & schema ?~ ref
+     in OpenApiHandler $ singletonNode (DocResponseBody defs mediaType body)
+
+instance ToSchema val => Get (OpenApiHandler m) (JSONBody val) Request where
+  {-# INLINEABLE getTrait #-}
+  getTrait :: JSONBody val -> OpenApiHandler m (Linked ts Request) (Either Text val)
+  getTrait (JSONBody maybeMediaType) = getTrait (Body @val maybeMediaType)
+
+instance ToSchema val => Set (OpenApiHandler m) (JSONBody val) Response where
+  {-# INLINEABLE setTrait #-}
+  setTrait ::
+    JSONBody val ->
+    (Linked ts Response -> Response -> t -> Linked (JSONBody val : ts) Response) ->
+    OpenApiHandler m (Linked ts Response, t) (Linked (JSONBody val : ts) Response)
+  setTrait (JSONBody maybeMediaType) _ =
+    let mediaType = fromMaybe "*/*" maybeMediaType
+        (defs, ref) = runDeclare (declareSchemaRef $ Proxy @val) mempty
+        body = mempty @MediaTypeObject & schema ?~ ref
+     in OpenApiHandler $ singletonNode (DocResponseBody defs mediaType body)
diff --git a/src/WebGear/OpenApi/Trait/Header.hs b/src/WebGear/OpenApi/Trait/Header.hs
new file mode 100644
--- /dev/null
+++ b/src/WebGear/OpenApi/Trait/Header.hs
@@ -0,0 +1,63 @@
+{-# OPTIONS_GHC -Wno-orphans #-}
+
+-- | OpenApi implementation of 'Header' trait.
+module WebGear.OpenApi.Trait.Header () where
+
+import Control.Lens ((&), (.~), (?~))
+import Data.OpenApi hiding (Response)
+import Data.Proxy (Proxy (Proxy))
+import Data.String (fromString)
+import Data.Text (Text)
+import GHC.TypeLits (KnownSymbol, symbolVal)
+import WebGear.Core.Modifiers (Existence (..))
+import WebGear.Core.Request (Request)
+import WebGear.Core.Response (Response)
+import WebGear.Core.Trait (Get (..), Set (..), Trait, TraitAbsence)
+import qualified WebGear.Core.Trait.Header as WG
+import WebGear.OpenApi.Handler (DocNode (..), OpenApiHandler (..), nullNode, singletonNode)
+
+mkParam ::
+  forall name val.
+  (KnownSymbol name, ToSchema val) =>
+  Proxy name ->
+  Proxy val ->
+  Bool ->
+  Param
+mkParam _ _ isRequired =
+  (mempty :: Param)
+    & name .~ fromString @Text (symbolVal $ Proxy @name)
+    & in_ .~ ParamHeader
+    & required ?~ isRequired
+    & schema ?~ Inline (toSchema $ Proxy @val)
+
+instance (KnownSymbol name, ToSchema val, TraitAbsence (WG.Header Required ps name val) Request) => Get (OpenApiHandler m) (WG.Header Required ps name val) Request where
+  {-# INLINEABLE getTrait #-}
+  getTrait WG.Header =
+    OpenApiHandler $ singletonNode (DocRequestHeader $ mkParam (Proxy @name) (Proxy @val) True)
+
+instance (KnownSymbol name, ToSchema val, TraitAbsence (WG.Header Optional ps name val) Request) => Get (OpenApiHandler m) (WG.Header Optional ps name val) Request where
+  {-# INLINEABLE getTrait #-}
+  getTrait WG.Header =
+    OpenApiHandler $ singletonNode (DocRequestHeader $ mkParam (Proxy @name) (Proxy @val) False)
+
+instance (KnownSymbol name, ToSchema val, Trait (WG.Header Required ps name val) Response) => Set (OpenApiHandler m) (WG.Header Required ps name val) Response where
+  {-# INLINEABLE setTrait #-}
+  setTrait WG.Header _ =
+    let headerName = fromString $ symbolVal $ Proxy @name
+        header =
+          mempty @Header
+            & required ?~ True
+            & schema ?~ Inline (toSchema $ Proxy @val)
+     in if headerName == "Content-Type"
+          then OpenApiHandler nullNode
+          else OpenApiHandler $ singletonNode (DocResponseHeader headerName header)
+
+instance (KnownSymbol name, ToSchema val, Trait (WG.Header Optional ps name val) Response) => Set (OpenApiHandler m) (WG.Header Optional ps name val) Response where
+  {-# INLINEABLE setTrait #-}
+  setTrait WG.Header _ =
+    let headerName = fromString $ symbolVal $ Proxy @name
+        header =
+          mempty @Header
+            & required ?~ True
+            & schema ?~ Inline (toSchema $ Proxy @val)
+     in OpenApiHandler $ singletonNode (DocResponseHeader headerName header)
diff --git a/src/WebGear/OpenApi/Trait/Method.hs b/src/WebGear/OpenApi/Trait/Method.hs
new file mode 100644
--- /dev/null
+++ b/src/WebGear/OpenApi/Trait/Method.hs
@@ -0,0 +1,13 @@
+{-# OPTIONS_GHC -Wno-orphans #-}
+
+-- | OpenApi implementation of 'Method' trait.
+module WebGear.OpenApi.Trait.Method where
+
+import WebGear.Core.Request (Request)
+import WebGear.Core.Trait (Get (..))
+import WebGear.Core.Trait.Method (Method (..))
+import WebGear.OpenApi.Handler (DocNode (DocMethod), OpenApiHandler (OpenApiHandler), singletonNode)
+
+instance Get (OpenApiHandler m) Method Request where
+  {-# INLINEABLE getTrait #-}
+  getTrait (Method method) = OpenApiHandler $ singletonNode (DocMethod method)
diff --git a/src/WebGear/OpenApi/Trait/Path.hs b/src/WebGear/OpenApi/Trait/Path.hs
new file mode 100644
--- /dev/null
+++ b/src/WebGear/OpenApi/Trait/Path.hs
@@ -0,0 +1,40 @@
+{-# OPTIONS_GHC -Wno-orphans #-}
+
+-- | OpenApi implementation of path traits.
+module WebGear.OpenApi.Trait.Path where
+
+import Data.Data (Proxy (Proxy))
+import Data.OpenApi (Param (..), ParamLocation (ParamPath), Referenced (Inline), ToSchema, toSchema)
+import Data.String (fromString)
+import GHC.TypeLits (KnownSymbol, symbolVal)
+import WebGear.Core.Request (Request)
+import WebGear.Core.Trait (Get (..), Linked)
+import WebGear.Core.Trait.Path (Path (..), PathEnd (..), PathVar (..), PathVarError (..))
+import WebGear.OpenApi.Handler (
+  DocNode (DocPathElem, DocPathVar),
+  OpenApiHandler (..),
+  singletonNode,
+ )
+
+instance Get (OpenApiHandler m) Path Request where
+  {-# INLINEABLE getTrait #-}
+  getTrait :: Path -> OpenApiHandler m (Linked ts Request) (Either () ())
+  getTrait (Path p) = OpenApiHandler $ singletonNode (DocPathElem p)
+
+instance (KnownSymbol tag, ToSchema val) => Get (OpenApiHandler m) (PathVar tag val) Request where
+  {-# INLINEABLE getTrait #-}
+  getTrait :: PathVar tag val -> OpenApiHandler m (Linked ts Request) (Either PathVarError val)
+  getTrait PathVar =
+    let param =
+          (mempty :: Param)
+            { _paramName = fromString $ symbolVal $ Proxy @tag
+            , _paramIn = ParamPath
+            , _paramRequired = Just True
+            , _paramSchema = Just $ Inline $ toSchema $ Proxy @val
+            }
+     in OpenApiHandler $ singletonNode (DocPathVar param)
+
+instance Get (OpenApiHandler m) PathEnd Request where
+  {-# INLINEABLE getTrait #-}
+  getTrait :: PathEnd -> OpenApiHandler m (Linked ts Request) (Either () ())
+  getTrait PathEnd = OpenApiHandler $ singletonNode (DocPathElem "/")
diff --git a/src/WebGear/OpenApi/Trait/QueryParam.hs b/src/WebGear/OpenApi/Trait/QueryParam.hs
new file mode 100644
--- /dev/null
+++ b/src/WebGear/OpenApi/Trait/QueryParam.hs
@@ -0,0 +1,44 @@
+{-# OPTIONS_GHC -Wno-orphans #-}
+
+-- | OpenApi implementation of 'QueryParam' trait.
+module WebGear.OpenApi.Trait.QueryParam where
+
+import Data.OpenApi (
+  Param (..),
+  ParamLocation (ParamQuery),
+  Referenced (Inline),
+  ToSchema,
+  toSchema,
+ )
+import Data.Proxy (Proxy (Proxy))
+import Data.String (fromString)
+import GHC.TypeLits (KnownSymbol, symbolVal)
+import WebGear.Core.Modifiers
+import WebGear.Core.Request (Request)
+import WebGear.Core.Trait (Get (..), TraitAbsence)
+import WebGear.Core.Trait.QueryParam (QueryParam (..))
+import WebGear.OpenApi.Handler (DocNode (DocQueryParam), OpenApiHandler (..), singletonNode)
+
+instance (KnownSymbol name, ToSchema val, TraitAbsence (QueryParam Required ps name val) Request) => Get (OpenApiHandler m) (QueryParam Required ps name val) Request where
+  {-# INLINEABLE getTrait #-}
+  getTrait _ =
+    let param =
+          (mempty :: Param)
+            { _paramName = fromString $ symbolVal $ Proxy @name
+            , _paramIn = ParamQuery
+            , _paramRequired = Just True
+            , _paramSchema = Just $ Inline $ toSchema $ Proxy @val
+            }
+     in OpenApiHandler $ singletonNode (DocQueryParam param)
+
+instance (KnownSymbol name, ToSchema val, TraitAbsence (QueryParam Optional ps name val) Request) => Get (OpenApiHandler m) (QueryParam Optional ps name val) Request where
+  {-# INLINEABLE getTrait #-}
+  getTrait _ =
+    let param =
+          (mempty :: Param)
+            { _paramName = fromString $ symbolVal $ Proxy @name
+            , _paramIn = ParamQuery
+            , _paramRequired = Just False
+            , _paramSchema = Just $ Inline $ toSchema $ Proxy @val
+            }
+     in OpenApiHandler $ singletonNode (DocQueryParam param)
diff --git a/src/WebGear/OpenApi/Trait/Status.hs b/src/WebGear/OpenApi/Trait/Status.hs
new file mode 100644
--- /dev/null
+++ b/src/WebGear/OpenApi/Trait/Status.hs
@@ -0,0 +1,18 @@
+{-# OPTIONS_GHC -Wno-orphans #-}
+
+-- | OpenApi implementation of 'Status' trait.
+module WebGear.OpenApi.Trait.Status where
+
+import qualified Network.HTTP.Types as HTTP
+import WebGear.Core.Response (Response)
+import WebGear.Core.Trait (Linked, Set, setTrait)
+import WebGear.Core.Trait.Status (Status (..))
+import WebGear.OpenApi.Handler (DocNode (DocStatus), OpenApiHandler (..), singletonNode)
+
+instance Set (OpenApiHandler m) Status Response where
+  {-# INLINEABLE setTrait #-}
+  setTrait ::
+    Status ->
+    (Linked ts Response -> Response -> HTTP.Status -> Linked (Status : ts) Response) ->
+    OpenApiHandler m (Linked ts Response, HTTP.Status) (Linked (Status : ts) Response)
+  setTrait (Status status) _ = OpenApiHandler $ singletonNode (DocStatus status)
diff --git a/src/WebGear/OpenApi/Traits.hs b/src/WebGear/OpenApi/Traits.hs
new file mode 100644
--- /dev/null
+++ b/src/WebGear/OpenApi/Traits.hs
@@ -0,0 +1,15 @@
+{- | OpenAPI implementation of all traits supported by WebGear.
+
+ This modules only exports orphan instances imported from other
+ modules. Hence the haddock documentation will be empty.
+-}
+module WebGear.OpenApi.Traits () where
+
+import WebGear.OpenApi.Trait.Auth.Basic ()
+import WebGear.OpenApi.Trait.Auth.JWT ()
+import WebGear.OpenApi.Trait.Body ()
+import WebGear.OpenApi.Trait.Header ()
+import WebGear.OpenApi.Trait.Method ()
+import WebGear.OpenApi.Trait.Path ()
+import WebGear.OpenApi.Trait.QueryParam ()
+import WebGear.OpenApi.Trait.Status ()
diff --git a/webgear-openapi.cabal b/webgear-openapi.cabal
new file mode 100644
--- /dev/null
+++ b/webgear-openapi.cabal
@@ -0,0 +1,92 @@
+cabal-version:       2.4
+
+name:                webgear-openapi
+version:             1.0.0
+synopsis:            Composable, type-safe library to build HTTP API servers
+description:
+    WebGear is a library to for building composable, type-safe HTTP API servers.
+    This package can be used to generate OpenAPI specifications from WebGear
+    applications.
+homepage:            https://github.com/haskell-webgear/webgear#readme
+bug-reports:         https://github.com/haskell-webgear/webgear/issues
+author:              Raghu Kaippully
+maintainer:          rkaippully@gmail.com
+copyright:           2020 Raghu Kaippully
+license:             MPL-2.0
+license-file:        LICENSE
+category:            Web
+build-type:          Simple
+extra-source-files:  README.md
+                     CHANGELOG.md
+
+
+source-repository head
+  type:      git
+  location:  https://github.com/haskell-webgear/webgear
+
+
+library
+  exposed-modules:    WebGear.OpenApi
+                    , WebGear.OpenApi.Handler
+                    , WebGear.OpenApi.Traits
+                    , WebGear.OpenApi.Trait.Auth.Basic
+                    , WebGear.OpenApi.Trait.Auth.JWT
+                    , WebGear.OpenApi.Trait.Body
+                    , WebGear.OpenApi.Trait.Header
+                    , WebGear.OpenApi.Trait.Method
+                    , WebGear.OpenApi.Trait.Path
+                    , WebGear.OpenApi.Trait.QueryParam
+                    , WebGear.OpenApi.Trait.Status
+  hs-source-dirs:     src
+  default-language:   Haskell2010
+  default-extensions: Arrows
+                      ConstraintKinds
+                      DataKinds
+                      DeriveFunctor
+                      DeriveGeneric
+                      DerivingStrategies
+                      DerivingVia
+                      FlexibleContexts
+                      FlexibleInstances
+                      FunctionalDependencies
+                      GeneralizedNewtypeDeriving
+                      InstanceSigs
+                      KindSignatures
+                      LambdaCase
+                      MultiParamTypeClasses
+                      NamedFieldPuns
+                      OverloadedStrings
+                      OverloadedLists
+                      PolyKinds
+                      RankNTypes
+                      RecordWildCards
+                      ScopedTypeVariables
+                      StandaloneDeriving
+                      TemplateHaskellQuotes
+                      TypeApplications
+                      TypeFamilies
+                      TypeOperators
+  build-depends:      arrows ==0.4.*
+                    , base >=4.13.0.0 && <4.17
+                    , http-media ==0.8.*
+                    , http-types ==0.12.*
+                    , insert-ordered-containers ==0.2.*
+                    , lens >=4.18.1 && <5.2
+                    , openapi3 ==3.1.*
+                    , text ==1.2.*
+                    , webgear-core ==1.0.0
+  ghc-options:        -Wall
+                      -Wno-unticked-promoted-constructors
+                      -Wcompat
+                      -Widentities
+                      -Wincomplete-record-updates
+                      -Wincomplete-uni-patterns
+                      -Wmissing-fields
+                      -Wmissing-home-modules
+                      -Wmissing-deriving-strategies
+                      -Wpartial-fields
+                      -Wredundant-constraints
+                      -fshow-warning-groups
+
+  if impl(ghc >= 8.10)
+    ghc-options:      -Wunused-packages
