diff --git a/CHANGELOG.md b/CHANGELOG.md
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,10 @@
 # Changelog
 
+## 0.1.1
+
+### Added
+- `sERVER_NOT_INITIALIZED` error code constant (-32002) in `MCP.Protocol`.
+
 ## 0.1.0
 
 ### Added
diff --git a/README.md b/README.md
new file mode 100644
--- /dev/null
+++ b/README.md
@@ -0,0 +1,56 @@
+# mcp-types — MCP protocol types for Haskell
+
+[![mcp-types on Hackage](https://img.shields.io/hackage/v/mcp-types.svg)](https://hackage.haskell.org/package/mcp-types)
+
+Core type definitions and JSON-RPC protocol layer for the
+[Model Context Protocol (MCP)](https://modelcontextprotocol.io/).
+
+This package contains only the pure protocol types with minimal dependencies,
+Implements MCP protocol version **2025-06-18**, making it suitable for
+building both clients and servers on any framework.
+For a ready-made Servant-based server, see the
+[`mcp`](https://hackage.haskell.org/package/mcp) package.
+
+## Modules
+
+- **`MCP.Types`** — Core MCP data types: Content, Resource, Tool, Prompt,
+  Capability, Implementation, and more.
+- **`MCP.Protocol`** — JSON-RPC 2.0 message wrappers, all client/server
+  request/response types, notification types, and protocol constants.
+  Re-exports the [`jsonrpc`](https://hackage.haskell.org/package/jsonrpc)
+  transport types.
+- **`MCP.Aeson`** — Custom Aeson parsing options used internally.
+
+## Install
+
+```cabal
+build-depends:
+    base
+  , aeson
+  , mcp-types
+```
+
+## MCP Protocol Support
+
+| Operation | Description |
+|-----------|-------------|
+| `initialize` | Start session and negotiate capabilities |
+| `ping` | Health check |
+| `resources/list` | List available resources |
+| `resources/templates/list` | List resource templates |
+| `resources/read` | Read resource contents |
+| `resources/subscribe` | Subscribe to resource updates |
+| `resources/unsubscribe` | Unsubscribe from resource updates |
+| `prompts/list` | List available prompts |
+| `prompts/get` | Get prompt with arguments |
+| `tools/list` | List available tools |
+| `tools/call` | Execute a tool |
+| `completion/complete` | Auto-completion with context |
+| `logging/setLevel` | Set logging level |
+| `sampling/createMessage` | Request LLM sampling |
+| `roots/list` | List client root directories |
+| `elicitation/create` | Request user input via forms |
+
+## License
+
+MPL-2.0
diff --git a/mcp-types.cabal b/mcp-types.cabal
--- a/mcp-types.cabal
+++ b/mcp-types.cabal
@@ -1,6 +1,6 @@
 cabal-version: 2.2
 name: mcp-types
-version: 0.1.0
+version: 0.1.1
 license: MPL-2.0
 license-file: LICENSE
 copyright: (c) 2025 DPella AB
@@ -8,6 +8,7 @@
 tested-with: ghc ==9.12.2
 extra-doc-files:
   CHANGELOG.md
+  README.md
 
 maintainer:
   matti@dpella.io,
diff --git a/src/MCP/Aeson.hs b/src/MCP/Aeson.hs
--- a/src/MCP/Aeson.hs
+++ b/src/MCP/Aeson.hs
@@ -1,6 +1,5 @@
 {- |
 Module:      MCP.Aeson
-Copyright:   (c) DPella AB 2025
 License:     MPL-2.0
 Maintainer:  <matti@dpella.io>, <lobo@dpella.io>
 -}
diff --git a/src/MCP/Protocol.hs b/src/MCP/Protocol.hs
--- a/src/MCP/Protocol.hs
+++ b/src/MCP/Protocol.hs
@@ -13,7 +13,6 @@
 {- |
 Module      : MCP.Protocol
 Description : MCP protocol types built on JSON-RPC 2.0
-Copyright   : (C) 2025 DPella AB
 License     : MPL-2.0
 Maintainer  : matti@dpella.io, lobo@dpella.io
 Stability   : experimental
@@ -106,6 +105,7 @@
 
     -- * MCP Constants
     pROTOCOL_VERSION,
+    sERVER_NOT_INITIALIZED,
 ) where
 
 import Control.Applicative ((<|>))
@@ -1119,6 +1119,10 @@
 -}
 pROTOCOL_VERSION :: Text
 pROTOCOL_VERSION = "2025-06-18"
+
+-- | JSON-RPC error code for requests received before the server has been initialized (-32002).
+sERVER_NOT_INITIALIZED :: Int
+sERVER_NOT_INITIALIZED = -32002
 
 {- | Primitive schema definitions that only allow primitive types without nested objects or arrays.
 
diff --git a/src/MCP/Types.hs b/src/MCP/Types.hs
--- a/src/MCP/Types.hs
+++ b/src/MCP/Types.hs
@@ -9,7 +9,6 @@
 {- |
 Module      : MCP.Types
 Description : Core types for the Model Context Protocol (MCP)
-Copyright   : (C) 2025 DPella AB
 License     : MPL-2.0
 Maintainer  : matti@dpella.io, lobo@dpella.io
 Stability   : experimental
@@ -22,6 +21,7 @@
 module MCP.Types (
     -- * Basic Types (re-exported from JSONRPC)
     RequestId (..),
+
     -- * Basic Types
     Role (..),
     Cursor (..),