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fix: align Context logging methods with MCP spec data type (#2366)

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Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>
Co-authored-by: Max Isbey <224885523+maxisbey@users.noreply.github.com>
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Gyeongjun Paik (Kent) 2026-04-15 06:41:51 +09:00 • committed by GitHub
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docs/migration.md
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@ -467,6 +467,26 @@ mcp._lowlevel_server._add_request_handler("resources/subscribe", handle_subscrib
This is a private API and may change. A public way to register these handlers on `MCPServer` is planned; until then, use this workaround or use the lowlevel `Server` directly.
### `MCPServer`'s `Context` logging: `message` renamed to `data`, `extra` removed
On the high-level `Context` object (`mcp.server.mcpserver.Context`), `log()`, `.debug()`, `.info()`, `.warning()`, and `.error()` now take `data: Any` instead of `message: str`, matching the MCP spec's `LoggingMessageNotificationParams.data` field which allows any JSON-serializable value. The `extra` parameter has been removed — pass structured data directly as `data`.
The lowlevel `ServerSession.send_log_message(data: Any)` already accepted arbitrary data and is unchanged.
`Context.log()` also now accepts all eight RFC-5424 log levels (`debug`, `info`, `notice`, `warning`, `error`, `critical`, `alert`, `emergency`) via the `LoggingLevel` type, not just the four it previously allowed.
```python
# Before
await ctx.info("Connection failed", extra={"host": "localhost", "port": 5432})
await ctx.log(level="info", message="hello")
# After
await ctx.info({"message": "Connection failed", "host": "localhost", "port": 5432})
await ctx.log(level="info", data="hello")
```
Positional calls (`await ctx.info("hello")`) are unaffected.
### Replace `RootModel` by union types with `TypeAdapter` validation
The following union types are no longer `RootModel` subclasses: