@frontmcp/protocol

@frontmcp/protocol

The single boundary between FrontMCP and the upstream @modelcontextprotocol/sdk.

Internal package. It is published so the other @frontmcp/* packages can resolve it — you should not import it from application code. Import MCP types from @frontmcp/sdk instead, and use McpClient from @frontmcp/testing for a raw client in tests.

Why it exists

libs/protocol/src/types.ts is the only file in the whole monorepo that transitively imports @modelcontextprotocol/sdk. Everything else — SDK, adapters, plugins, auth, tests — imports from @frontmcp/protocol.

That indirection means swapping, pinning, or dropping the upstream package is a one-file change instead of a repo-wide refactor. The @nx/dependency-checks lint rule enforces it: adding a direct upstream import anywhere else fails the build.

✅ Route through the boundary:

import { CallToolRequestSchema, McpError, type Tool } from '@frontmcp/protocol';

❌ Never import the upstream package directly — that locks every call site to it:

import { McpError } from '@modelcontextprotocol/sdk/types.js';

If a type you need is not reachable from @frontmcp/protocol, re-export it from libs/protocol/src/types.ts rather than reaching around the boundary.

What it exports

Area	Contents
Protocol types	Requests, results, notifications, schemas, McpError, capabilities
Protocol 2026-07-28	Types the upstream SDK does not ship yet — see below
Server	McpServer, StreamableHTTPServerTransport, WebStandardStreamableHTTPServerTransport
Client	Client, StreamableHTTPClientTransport, SSEClientTransport
Transports	stdio (Node + browser), in-memory
Auth types	AuthInfo and friends

Node and browser/worker variants are selected automatically through package subpath imports, so the same import works in every runtime FrontMCP targets.

Protocol 2026-07-28

The upstream SDK tops out at 2025-11-25. Revision 2026-07-28 is therefore defined here — MCP_20260728_META, MCP_20260728_ERROR_CODES, CacheableResult, DiscoverResult, InputRequiredResult, SubscriptionFilter, and the rest.

Everything is additive: the 2025-and-earlier types are untouched, because a FrontMCP server serves both eras on the same endpoint. When upstream catches up, types-20260728.ts is the only file that has to change.

See the protocol versions guide for what the revision changed and how FrontMCP selects one per request.

License

Apache-2.0