Reason Plugins MCP Server

Reason plugins for Claude Code and Codex

Connect a coding agent to your Reason workspace at https://mcp.reasonmachines.com/mcp. Sign in through your browser, choose a workspace, review permissions, and connect. The plugin contains no API key, credential, local executable or hook.

Install the Reason plugin

Claude Code

claude plugin marketplace add reason-machines/reason-plugins
claude plugin install reason@reason

Open /mcp in Claude Code and authenticate Reason when prompted.

Codex

codex plugin marketplace add reason-machines/reason-plugins
codex plugin add reason@reason

Enable Reason and complete the browser authentication prompt. Reload the client if its tool list was already open when you installed the plugin.

These are Reason Machines' publisher-owned plugins. Installation does not depend on acceptance into Anthropic's curated marketplace or OpenAI's public directory; those services review and approve listings separately.

Cursor

Add Reason to Cursor

For privacy details, see the Privacy Policy and Terms of Service. For support, contact contact@reasonmachines.com.

In the Codex app, open Plugins → Add → Add plugin marketplace, paste https://github.com/reason-machines/reason-plugins, and add the marketplace. Leave Git ref and Sparse paths empty. Select Reason MCP → Install, then complete the browser authentication prompt. No separate MCP configuration is needed.

The marketplace identifier is reason.

Moving from the Ara plugin

Reason was called Ara, and this repository was Aradotso/ara-mcp. The ara plugin (and ara-handoff before it) connected to a server that is now retired: https://api.ara.so/mcp/ara answers HTTP 410. The reason plugin replaces both.

Claude Code

If you added the marketplace under its old name, it is still registered as ara on your machine. Refresh it and install the plugin under its new name:

claude plugin marketplace update ara
claude plugin install reason@ara

Then open /mcp and authenticate Reason. After the refresh Claude Code no longer loads the retired server and moves your ara@ara (or ara-handoff@ara) setting to reason@ara; the install fetches the plugin itself.

Codex

Codex keeps serving an installed plugin until you remove it, so remove the old one and add the new one:

codex plugin remove ara@ara
codex plugin marketplace remove ara
codex plugin marketplace add reason-machines/reason-plugins
codex plugin add reason@reason

Cursor and other clients

Delete the ara entry whose URL ends in /mcp/ara from your MCP configuration (~/.cursor/mcp.json for Cursor) and add the server shown under Other MCP clients.

If you have the Reason CLI, reason mcp uninstall removes the retired registrations from Claude Code, Codex and Cursor in one step.

More from Reason

• reason-agent: what Reason Agent is, how to use it, releases and benchmarks.
• reason-cli: the reason command line.
• reason-marketplace: every plugin and connector Reason can use inside your workspace.

Connect without a plugin

Claude Code

claude mcp add --transport http reason https://mcp.reasonmachines.com/mcp

Then open /mcp and authenticate Reason.

Codex

codex mcp add reason --url https://mcp.reasonmachines.com/mcp
codex mcp login reason

Other MCP clients

Choose a remote Streamable HTTP server with URL https://mcp.reasonmachines.com/mcp and OAuth authentication. For example:

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

For headless integrations, a scoped Reason API key can be provided by your client's secret manager as an Authorization bearer header. Never put a token in this repository, a prompt, a shared configuration file, or a URL. OAuth credentials are audience-bound: a REST login cannot be reused as an MCP login.

Try it

• “Show my Reason projects and recent sessions.”
• “Create a project for this repository and add these instructions.”
• “Find my session about the billing bug and show its latest messages.”
• “Archive this project, then restore it.”

The tools follow the active public v3 contract and your granted scopes. Start with getSelf to check the connected workspace. Path and query arguments are top-level; JSON request bodies go in body. Workspace selection is automatic and pinned to the connection.

For example, listProjects accepts {"archived":"include"}. updateProject accepts {"projectId":"…","body":{"project_md":{"content":"…","expected_revision":1}}}. Read the current project_document.revision with getProject first. A stale revision returns 409, preserving the newer instructions.

Creating a session starts asynchronous work; inspect its status before assuming it finished. Follow pagination cursors for complete lists. Tool results preserve API status and data, including permission errors, conflicts and rate limits.

All active v3 operations are represented. Deprecated compatibility aliases and retired routes are omitted. File uploads take body.filename and body.data_base64, limited to 1 MiB; use REST for larger uploads. Downloads return an authorized download_url, never forward your Reason bearer to that URL. Large results are bounded at 2 MiB; request a smaller page or use REST.

Permissions and disconnection

Each connection is bound to the workspace chosen during consent. Tools reuse the API's scope, membership, role, private-project and IP access checks. Stored secrets remain write-only. MCP does not grant arbitrary control of your Mac or bypass a service's OAuth approval. Revoking a connection or removing its workspace membership stops access. Use your client's disconnect/logout controls and Reason's connected-app controls when the integration is no longer needed.

Support and validation

Contact Reason Machines. See SECURITY.md for vulnerability reporting.

claude plugin validate --strict plugins/reason
claude plugin validate --strict .claude-plugin/marketplace.json

python3 -m unittest discover -s tests installs the package with the Codex CLI and checks the manifests, the renames map for former plugin names, and server.json, the entry for the MCP Registry. Publish that entry by running the Publish to MCP Registry workflow by hand; to publish a change, raise version in server.json first.

Validate the Codex manifest with the Codex plugin validator. Test installations in an isolated client configuration directory, preserving personal installations. Production connection and directory approval are separate from manifest validation.