Add settings and environment variables reference#3384
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jlowin
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| FastMCP uses [pydantic-settings](https://docs.pydantic.dev/latest/concepts/pydantic_settings/) for configuration. Every setting is available as an environment variable with a `FASTMCP_` prefix, loaded automatically from the environment or a `.env` file. |
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.env
Settings loads dotenv values through Settings.model_config.env_file in src/fastmcp/settings.py, but Docket config is a pre-instantiated DocketSettings() field (Settings.docket) whose own model_config only defines an FASTMCP_DOCKET_ prefix and no env_file. As written, this sentence implies .env values work for every setting, but users who put FASTMCP_DOCKET_URL in .env can still end up on the default memory:// backend, which is a high-impact misconfiguration for multi-worker task deployments.
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FastMCP has ~30 configurable settings available as
FASTMCP_*environment variables via pydantic-settings, but until now you had to readsrc/fastmcp/settings.pyto discover them. This adds a dedicated reference page atmore/settingsthat groups everything by concern (logging, transport, error handling, client, CLI, tasks, advanced) with precise types, defaults, and descriptions.Also adds a maintenance note to CLAUDE.md so future settings changes stay in sync with the doc.
Closes #3275