The official Python SDK for Model Context Protocol servers and clients
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# Versioning Policy
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The MCP Python SDK (`mcp`) follows [Semantic Versioning 2.0.0](https://semver.org/).
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## Version Format
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`MAJOR.MINOR.PATCH`
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- **MAJOR**: Incremented for breaking changes (see below).
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- **MINOR**: Incremented for new features that are backward-compatible.
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- **PATCH**: Incremented for backward-compatible bug fixes.
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## What Constitutes a Breaking Change
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The following changes are considered breaking and require a major version bump:
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- Removing or renaming a public API export (class, function, type, or constant).
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- Changing the signature of a public function or method in a way that breaks existing callers (removing parameters, changing required/optional status, changing types).
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- Removing or renaming a public type or dataclass/TypedDict field.
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- Changing the behavior of an existing API in a way that breaks documented contracts.
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- Dropping support for a Python version that is still receiving security updates.
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- Removing support for a transport type.
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- Changes to the MCP protocol version that require client/server code changes.
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The following are **not** considered breaking:
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- Adding new optional parameters to existing functions.
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- Adding new exports, types, or classes.
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- Adding new optional fields to existing types.
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- Bug fixes that correct behavior to match documented intent.
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- Internal refactoring that does not affect the public API.
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- Adding support for new MCP spec features.
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- Changes to dev dependencies or build tooling.
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## How Breaking Changes Are Communicated
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1. **Changelog**: All breaking changes are documented in the GitHub release notes with migration instructions.
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2. **Deprecation**: When feasible, APIs are deprecated for at least one minor release before removal using `warnings.warn()` with `DeprecationWarning`, which surfaces warnings at runtime and through static analysis tooling.
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3. **Migration guide**: Major version releases include a migration guide describing what changed and how to update.
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4. **PR labels**: Pull requests containing breaking changes are labeled with `breaking change`.
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