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v4.20.17

punkpeye/fastmcpv4.20.17Sep 24, 2026by github-actions[bot]

Upgrading?

What changed from v31.5.2 → v4.20.17?What's new in v4.20.18 after v4.20.17?

AI Summary

This release focuses on bug fixes, including correcting error responses for missing prompt arguments, fixing CLI validation path handling, and ensuring tool visibility for unauthenticated sessions. It also improves OpenAPI schema generation by preserving types for non-nullable fields.

Key Highlights

  • Fixes error code -32602 for prompts requested without required arguments
  • Resolves CLI validate command splicing file paths incorrectly
  • Ensures canAccess tools remain visible to unauthenticated sessions after runtime changes
  • Preserves schema types in OpenAPI when nullable is false

Full Release Notes

## [4.20.17](https://github.com/punkpeye/fastmcp/compare/v4.20.16...v4.20.17) (2026-09-24)


### Bug Fixes

* answer -32602 when a prompt is requested without a required argument ([#390](https://github.com/punkpeye/fastmcp/issues/390)) ([25046a2](https://github.com/punkpeye/fastmcp/commit/25046a2c4ad2a7ca71e89723f266253ab593ba57))
* **cli:** stop splicing the file path into the validate commands ([#388](https://github.com/punkpeye/fastmcp/issues/388)) ([c130336](https://github.com/punkpeye/fastmcp/commit/c1303364d111112f1f8ca05ff5908916b31c7b3a))
* keep canAccess tools visible to sessions without auth after a runtime change ([#389](https://github.com/punkpeye/fastmcp/issues/389)) ([91b6d8b](https://github.com/punkpeye/fastmcp/commit/91b6d8be62c84d3101836cd24475acf210fd7ed4))
* **openapi:** preserve schema types when nullable is false ([#387](https://github.com/punkpeye/fastmcp/issues/387)) ([89a7516](https://github.com/punkpeye/fastmcp/commit/89a7516beabbe5d7ea7f591c736f02aeccc50ff2))

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