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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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11
docs/client/index.md
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@ -81,7 +81,7 @@ That schema is everything a UI needs to render an argument form, and everything
`call_tool(name, arguments)` runs the tool and gives you back a `CallToolResult`.
```python title="client.py" hl_lines="26-33"
```python title="client.py" hl_lines="27-34"
--8<-- "docs_src/client/tutorial003.py"
```
@ -113,7 +113,7 @@ A tool that raises does **not** raise in your client. It comes back as an ordina
!!! check
Ask `lookup_book` for `"Solaris"` (a title that isn't in the catalog) and the function raises
`ValueError`. The call still returns normally:
`ToolError`. The call still returns normally:
```python
result.is_error # True
@ -121,9 +121,10 @@ A tool that raises does **not** raise in your client. It comes back as an ordina
result.structured_content # None
```
The exception's message landed in `content`, where the **model** can read it and try again. That
is deliberate: a tool error is part of the conversation, not a crash. Always look at `is_error`
before you trust `structured_content`.
The `ToolError`'s message landed in `content`, where the **model** can read it and try again. That
is deliberate: a tool error is part of the conversation, not a crash. (Had the tool crashed with
some other exception, `content` would say only `Error executing tool lookup_book`.) Always look at
`is_error` before you trust `structured_content`.
!!! warning
`is_error=True` covers more than your own `raise`. Ask for a tool the server doesn't even have