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mcptools 1.0.0

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@simonpcouch simonpcouch released this 05 Jul 18:03
v1.0.0
9c9217a

mcp_server()

New features:

  • mcptools can now run as a Posit Connect R API engine. Add a _server.yml with engine: mcptools, point tools to an .R file returning ellmer::tool() objects, and deploy with rsconnect::deployAPI(".", contentCategory = "mcp").

  • mcp_server() can now return inline image content from tools that produce ellmer::ContentImageInline results, including mixed text and image content (#96, #102).

  • mcp_server() now returns structuredContent alongside serialized JSON text for successful tool results that are naturally represented as JSON objects, when using MCP protocol version 2025-06-18 or later (#104).

  • mcp_server() now includes ellmer tool annotations in tools/list responses, preserving MCP safety hints such as title, readOnlyHint, destructiveHint, idempotentHint, and openWorldHint (#100, #105).

Bug fixes:

  • HTTP mcp_server() requests now honor the MCP-Protocol-Version header, return 400 Bad Request for unsupported protocol versions, and no longer let protocol negotiation from one HTTP client shape responses for another.

  • JSON output now serializes R NULL values as JSON null, fixing JSON-RPC responses with null request IDs.

  • mcp_server() no longer falls through after reporting Invalid Request for invalid stdio client messages.

  • Forwarded mcp_session() tool calls now return JSON-RPC errors when the selected R session does not respond within two minutes, rather than hanging indefinitely. Configure the timeout with the mcptools.session_response_timeout_seconds option or the MCPTOOLS_SESSION_RESPONSE_TIMEOUT_SECONDS environment variable. Session receive errors are also logged instead of silently discarded (#98).

mcp_tools()

New features:

  • mcp_tools() can now connect directly to remote Streamable HTTP MCP servers, configured with url instead of command. Static headers are supported for token auth, and full OAuth 2.1 (authorization-server discovery, Dynamic Client Registration, PKCE, and automatic token refresh) is handled via httr2, which also caches tokens across sessions (#88).

  • mcp_tools() now converts MCP tool-result content blocks into ellmer-native text and image content, allowing ellmer chats to receive image results from MCP tools.

Bug fixes:

  • mcp_tools() now launches MCP server processes with an allowlisted environment plus configured env variables. Previously, servers without configured env inherited the full R process environment, while servers with configured env received only those variables. The new behavior more closely matches reference MCP SDKs, reduces accidental credential exposure, and fixes Windows startup failures when env is configured. Servers that need additional non-allowlisted variables should list them in env (#62).
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