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Log MCPServer handler exceptions by kind and keep crash details off the wire (#3314)

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Co-authored-by: Marcelo Trylesinski <marcelotryle@gmail.com>
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Max 2026-08-24 15:51:18 +01:00 • committed by GitHub
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docs/deprecated.md
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@ -1,6 +1,6 @@
# Deprecated features
The 2026-07-28 spec retires five things. The SDK still implements every one of them, and every one of them now carries a **deprecation warning**.
The 2026-07-28 spec retires five things. The SDK still implements every one of them, and every one of them now carries a **deprecation warning**. One SDK helper is deprecated on its own account and is listed [at the end](#deprecated-sdk-helpers).
The table below names each deprecated feature, why it is going away, and the replacement to build on.
@ -119,15 +119,24 @@ That is the whole API. There is no per-method switch, and you don't want one: th
Run the filter the other way and you get a free regression test. Add
`"error::mcp.MCPDeprecationWarning"` to the `filterwarnings` setting in your pytest
configuration and the deprecated call **raises** instead of warning. A tool named
`old_log` that still calls `ctx.info()` stops passing and starts reporting:
`old_log` that still calls `ctx.info()` stops passing: the call comes back `is_error=True` with
`Error executing tool old_log`, and the captured server log names the culprit:
```text
Error executing tool old_log: The logging capability is deprecated as of 2026-07-28 (SEP-2577).
mcp.shared.exceptions.MCPDeprecationWarning: The logging capability is deprecated as of 2026-07-28 (SEP-2577).
```
One line of pytest configuration, and a deprecated call can never sneak back into your
codebase without failing a test.
## Deprecated SDK helpers
These are not spec changes, only SDK internals with a better replacement. They warn with the same `MCPDeprecationWarning` and will be removed in 3.0.
| Deprecated | What you do instead |
|---|---|
| `FuncMetadata.call_fn_with_arg_validation()` | `FuncMetadata.validate_arguments()` and then `FuncMetadata.call_fn()`. Only code that drives `FuncMetadata` directly (a custom `Tool` subclass, say) ever called it. |
## Recap
* The 2026-07-28 spec deprecates **roots**, server-initiated **sampling**, and protocol **logging** (all [SEP-2577](https://github.com/modelcontextprotocol/modelcontextprotocol/pull/2577)), restricts **progress** to server-to-client, and removes **`ping`**.
@ -135,6 +144,7 @@ That is the whole API. There is no per-method switch, and you don't want one: th
* Deprecated is advisory: no wire changes, everything keeps working against pre-2026 sessions, and you get a visible `MCPDeprecationWarning` (a `UserWarning`, so it is on by default).
* Sampling and roots additionally need a back-channel that a 2026-07-28 session does not have. On a modern connection they warn and then they raise.
* `warnings.filterwarnings("ignore", category=MCPDeprecationWarning)` silences the whole category; `"error::mcp.MCPDeprecationWarning"` in pytest turns it into a test failure.
* One SDK helper, `FuncMetadata.call_fn_with_arg_validation()`, is deprecated separately for removal in 3.0.
* New code should not be built on any of these.
Every other page in these docs teaches the current API.