Reason

What Reason does

The Reason MCP server gives compatible coding agents access to projects and sessions in a Reason workspace. It connects to https://mcp.reasonmachines.com/mcp and lets an agent inspect the connected identity, find projects, maintain project instructions, and work with coding-agent sessions.

The connection is associated with the workspace selected during browser consent. Access remains subject to Reason scopes, workspace membership, roles, private-project permissions, and any IP access controls. The server follows the active public v3 contract rather than exposing deprecated aliases or retired routes.

How it works

Reason uses remote Streamable HTTP transport. For normal interactive use, install the plugin in Claude Code, Codex, or Cursor, then complete the browser authentication flow. Other MCP clients can use the same remote URL with OAuth support. Claude Code and Codex can also add the endpoint directly without installing the plugin.

Workspace selection happens during consent and is pinned to the connection. Start with getSelf to confirm which workspace and identity are connected. Tool arguments use top-level path and query fields, while JSON request payloads are placed in body.

Session creation starts asynchronous work, so an agent should check the session status instead of assuming completion. List operations may return pagination cursors; following them is necessary for complete results. Responses retain API status and data, including permission failures, conflicts, and rate-limit responses.

Setup and configuration

In Claude Code, add the Reason plugin from the reason-machines/reason-plugins marketplace, install reason@reason, and authenticate through /mcp. In Codex, add the same marketplace and install reason@reason, then approve the browser prompt. Cursor provides a direct MCP installation link in the project documentation.

A client that supports remote MCP servers can instead use this configuration:

{
  "mcpServers": {
    "reason": {
      "type": "http",
      "url": "https://mcp.reasonmachines.com/mcp"
    }
  }
}

Headless deployments may provide a scoped Reason API key through the client's secret manager as an Authorization bearer header. Credentials should not be stored in prompts, shared configuration files, repository content, or URLs. OAuth credentials for REST access cannot be reused as MCP credentials.

Tools and capabilities

The Reason MCP server represents the active v3 operations, including:

• getSelf for checking the connected workspace and identity.
• listProjects for finding projects, with an option such as archived: "include".
• getProject for reading current project data and its document revision.
• updateProject for changing project instructions while supplying the expected revision.
• Session creation and session inspection for starting asynchronous coding-agent work and reviewing its state.
• Session message access for finding and reading conversation history.
• Project archive and restore operations.

Project-document updates use revision checking. An agent should read the current revision with getProject before writing; a stale revision produces a conflict instead of overwriting newer instructions.

Limitations and notes

File uploads accept body.filename and body.data_base64 and are limited to 1 MiB. Larger uploads should use REST. Downloads return an authorized download_url; the Reason bearer token must not be forwarded to that URL. MCP results are capped at 2 MiB, so large queries should use smaller pages or REST.

The Reason MCP server does not provide arbitrary control of a local computer or bypass OAuth approval. Revoking the connection or losing workspace membership removes access. Disconnect through the MCP client and Reason's connected-app controls when the integration is no longer required.

This listing belongs to the Coding Agents category and is intended for clients that can authenticate to the remote endpoint. The former Ara endpoint is retired; configurations still pointing to /mcp/ara must be removed or replaced with the Reason endpoint.