fastmcp Releases

Significantly strengthens security by tightening OAuth handling, file permissions, and input validation to protect against injection and permission issues.

Aug 26, 2026

A major update featuring a reworked MCP server, RAG-ready Markdown capabilities, improved Cloudflare solving, and browser tab reuse for automation.

Aug 23, 2026

This release resolves a bug in the edge implementation where a detached replay session would not be cleaned up if the parent session ended while the replay was still running. It ensures proper resource management by dropping these detached sessions to prevent memory leaks or state inconsistencies.

Aug 21, 2026

This update fixes an edge case in the reconnection logic where the system failed to answer reconnections that required replaying events to catch up on missed data. It ensures that users remain in sync with the server state by processing necessary replay events during the reconnection process.

Aug 21, 2026

This release addresses a stream conflict issue where a replayed stream would collide with an already live stream. It prevents potential data corruption or race conditions by rejecting replay attempts that conflict with active live streams.

Aug 21, 2026

This release fixes a resource cleanup issue where unread response bodies were not being canceled during fetch errors.

Aug 19, 2026

Addresses an edge case where JSON-mode POST requests are left hanging without an answer.

Aug 17, 2026

Improves stability by refining routing state handling and optimizing SSE event persistence logic.

Aug 17, 2026

Fixes the handling of Server-Sent Events (SSE) responses that arrive after a client has disconnected.

Aug 17, 2026

Ensures the resource-templates handler is correctly registered whenever resources are advertised to the system.

Aug 17, 2026

Introduces support for cancellation and timeouts in tool execution by passing an AbortSignal to the execution context.

Aug 17, 2026

Ensures that session identifiers remain valid even if the underlying transport connection is terminated prematurely.

Aug 17, 2026

Adjusts the session resolution logic to use the transport layer instead of resolving identifiers at the connection phase.

Aug 17, 2026

Simplifies the dependency tree by removing the direct undici dependency in favor of the global fetch API.

Aug 12, 2026

Fixes stream handling for batch requests and introduces a new feature allowing server icons to be exposed in options.

Aug 12, 2026

Fixes a validation issue in the edge environment to ensure tool arguments are checked before execution to prevent potential runtime errors.

Aug 11, 2026

Addresses issues with Server-Sent Events (SSE) responses and concurrent POST requests to ensure proper stream handling and response management.

Aug 11, 2026

A maintenance release focused on fixing installation issues with the `uv` package manager.

Aug 10, 2026

Corrects the schema precedence logic for tool outputs to ensure the correct schema is used when determining result types.

Aug 10, 2026

Improves completion handling by truncating overly long lists of values instead of causing the operation to fail.

Aug 10, 2026