fastmcp/docs
Jeremiah Lowin 41ec7ee06d
SEP-1577: Sampling with tools (#2551)
* MCP → SDK (vocab change only)

* WIP: Sampling API with SamplingResult[T] and result_type

* SEP-1577: Sampling with tools

- Add tools and result_type parameters to ctx.sample()
- Update OpenAI handler for tool content types
- Client advertises sampling.tools capability by default
- Collect tool results into single message with list content

* Fix tool result content handling in OpenAI handler

* Remove @sampling_tool decorator - pass functions directly to sample()

Functions passed to ctx.sample(tools=[...]) are now auto-converted
via SamplingTool.from_function(). Users can still use that method
directly for custom name/description overrides.

* Remove auto-conversion of MCP tools to sampling tools

Users want MCP tools passed to ctx.sample() to go through the full MCP
machinery (middleware, native responses) rather than being auto-converted
to direct function calls. Now only SamplingTool and plain callables are
accepted - passing a FastMCP Tool raises a clear TypeError.

Also bumps mcp dependency to >=1.24.0 for required sampling features.

* Refactor sampling API: replace sample_iter() with sample_step()

Replace the mutable SampleRun/sample_iter() pattern with a simpler stateless
sample_step() function. sample_step() makes a single LLM call and returns a
SampleStep with the response and history. sample() now loops sample_step()
internally.

Key changes:
- Add sample_step() for fine-grained control over the sampling loop
- Remove SampleRun class and sample_iter() method
- Structured output uses tool description only (no prompt modification)
- execute_tools parameter controls automatic vs manual tool execution

* Address CodeRabbit nitpicks

* Address CodeRabbit review feedback for sampling tools

- Fix temperature=0.0 being dropped due to falsy evaluation
- Add ToolChoice.name support for forcing specific tools
- Replace assert statements with explicit RuntimeError checks
- Add mask_error_details parameter to sample()/sample_step() with ToolError escape hatch
- Fix hasattr patterns with proper isinstance checks
- Document mask_error_details and add OpenAI prerequisites to docs

* Address additional CodeRabbit review feedback

- Catch ValidationError specifically instead of bare Exception
- Update result_type docs to mention dataclasses and basic types
- Raise ValueError for unknown tool_choice modes
- Validate sampling_handler_behavior to catch typos
- Remove ToolChoice.name handling (not part of MCP spec)
- Validate tool_choice string in sample_step()

* Review fixes for sampling tools PR

- Remove internal functions from sampling __init__.py exports
- Remove fragile is_text property, use not is_tool_use instead
- Inline call_client into context.py, remove from run.py
- Fix SamplingMessage docs to use TextContent
- Handle result.text being None in doc examples
- Simplify client sampling docs to recommend OpenAISamplingHandler
- Add sampling_capabilities override documentation
- Raise iteration limit from 50 to 100
- Remove _parse_model_preferences duplication
- Use AsyncOpenAI in OpenAISamplingHandler
- Fix tool_choice docstring

* Fix OpenAI handler tests to use AsyncOpenAI

* Address remaining CodeRabbit review comments

- Fix message ordering in OpenAI handler: tool results now correctly
  follow assistant message with tool_calls
- sample_step() now always includes assistant message in history
- Raise ValueError on JSON parse errors instead of silent {}
- Add has_sampling capability check when behavior is None
- Raise RuntimeError when structured output receives text response
- Wrap primitive result_type schemas in object wrapper
- Fix docs example using invalid SamplingMessage construction
- Add comprehensive client_sampling_test.py example

* Add return type annotation to OpenAISamplingHandler.__init__

* Use explicit 'is not None' check for sampling_capabilities defaulting

---------

Co-authored-by: claude[bot] <41898282+claude[bot]@users.noreply.github.com>
Co-authored-by: Bill Easton <strawgate@users.noreply.github.com>
2025-12-14 13:51:05 -05:00
..
.cursor/rules Clean up parameter documentation 2025-06-22 20:59:53 -04:00
assets Support custom server name, icons, and link in OAuth Proxy consent page (#2135) 2025-10-18 11:49:26 -04:00
clients SEP-1577: Sampling with tools (#2551) 2025-12-14 13:51:05 -05:00
community Update docs (#2094) 2025-10-14 16:38:21 -07:00
css Update VersionBadge to use Mintlify native Badge component (#2571) 2025-12-06 21:23:53 -05:00
deployment SEP-1699: Add SSE polling support with EventStore (#2564) 2025-12-09 09:55:51 -05:00
development Add v2.14.0 upgrade guide (#2565) 2025-12-06 11:40:42 -05:00
getting-started Pin Cyclopts to v4.0.0 + compliance note (#2354) 2025-11-03 18:37:12 -05:00
integrations Add supabase docs (#2030) 2025-12-04 18:25:57 -05:00
patterns docs: clarify pytest-asyncio dependency and asyncio mode configuration (#2399) 2025-11-15 10:34:29 -05:00
public/schemas/fastmcp.json chore: Update fastmcp.json schema (#1955) 2025-09-29 20:12:24 -04:00
python-sdk chore: Update SDK documentation (#2592) 2025-12-11 21:43:51 -05:00
servers SEP-1577: Sampling with tools (#2551) 2025-12-14 13:51:05 -05:00
snippets Update VersionBadge to use Mintlify native Badge component (#2571) 2025-12-06 21:23:53 -05:00
tutorials Remove trailing slashes from MCP endpoint URLs in docs (#2277) 2025-10-27 10:36:47 -04:00
.ccignore Add comprehensive OAuth 2.1 authentication system with WorkOS integration (#1327) 2025-08-01 17:06:55 -04:00
changelog.mdx 2.14 deprecation removals (#2329) 2025-12-01 14:11:00 -05:00
docs.json chore: Update SDK documentation (#2517) 2025-12-09 21:07:20 -05:00
updates.mdx Stage 2.13.0 updates (#2252) 2025-10-25 08:52:21 -04:00