Reason 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.

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

Shortened. The full README is on GitHub.