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MCP endpoints are in beta.
An MCP endpoint is a remote, authenticated Model Context Protocol server that your Bijection app defines and serves. It gives an external AI agent a small, explicit set of tools: the queries it may read and the business operations it may request. Everything else in your app stays out of reach. This is different from the Bijection MCP server, which the CLI runs on your machine so coding agents can inspect and develop your deployment. An MCP endpoint is part of your app and serves your app’s users.
bijection/mcp.ts
defineMcpServer takes an async function that returns the definition, because makeOperationReference is asynchronous. The function runs for each request. Each tool wraps a function you already have. A query tool runs your public query as the calling agent. An operation tool requests your operation through its ordinary invocation path, so your validators, access rules, transactions, approvals and recovery apply exactly as they do for any other client. The endpoint adds no second way to read or write your data.

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How it works

An MCP endpoint is built from pieces you write in your bijection/ folder:
  • Tools. mcpQuery, mcpOperation and mcpOperationStatus select existing functions and derive each tool’s input and output schemas from their validators.
  • A grant query. Your authorize query decides who the caller is acting for and which tools they may use. Publishing a tool grants nothing by itself.
  • Admission. Two mutations you write enforce rate and concurrency limits in your own tables.
  • Dispatch. An internal query and an internal mutation run each tool call, so the publication check, the grant check and the business work share one transaction.
  • Routes. You mount the endpoint and its OAuth metadata as HTTP actions.
Agents connect with a bearer token from the identity provider you already configured for authentication.

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Where it is served

MCP endpoints are served from the same host as your HTTP actions, https://<your deployment name>.bijection.site. Each endpoint URL ends with the publication revision, a digest of your deployed code and the endpoint’s definition:
When you push new code, the revision changes and the old URL stops answering with a 409 publication_changed response, so an agent cannot call tools on code that changed after it discovered them. See Defining MCP endpoints for how to mount the routes and read the current revision.

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What an endpoint exposes

An MCP endpoint publishes tools only. It answers initialize, ping, tools/list and tools/call with fixed JSON responses. It does not offer MCP resources, prompts, subscriptions, streaming, or arbitrary queries over your data.

Defining MCP endpoints

Select tools, write the dispatch and admission functions, and mount the routes.

Authentication and grants

Accept tokens from your identity provider and decide what each agent may do.

Connecting clients

Call the endpoint from an MCP client, and make writes recoverable with bijection/mcp/node.

Limits

Size bounds, supported methods and error codes.