Python: [BREAKING] Add sampling guardrails to MCP tools (#6413)

* Add sampling guardrails to MCP tools

Add approval, token, and request-count controls to the MCP sampling
callback used when an MCPTool is configured with a chat client.

- Add `sampling_approval_callback`, `sampling_max_tokens`, and
  `sampling_max_requests` parameters to `MCPTool` and its
  `MCPStdioTool`, `MCPStreamableHTTPTool`, and `MCPWebsocketTool`
  subclasses, positioned directly after `client`.
- Gate each server-initiated `sampling/createMessage` request behind the
  approval callback, which denies by default when no callback is provided.
- Clamp the requested `maxTokens` to `sampling_max_tokens` and enforce a
  per-session request count via `sampling_max_requests`.
- Log incoming sampling requests at WARNING level (counts only).
- Export `SamplingApprovalCallback` from the public API.
- Add tests, a sample, and documentation updates.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* Make sampling denial message context-aware

Distinguish the deny-by-default case (no approval callback configured)
from an explicit denial by a configured `sampling_approval_callback`, so
the returned ErrorData message is accurate for callback-driven denials
and exceptions.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

---------

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
This commit is contained in:
Eduard van Valkenburg
2026-06-10 10:17:36 +00:00
committed by GitHub
co-authored by Copilot
parent cea83bd8d5
commit 9a56bc9f16
6 changed files with 476 additions and 29 deletions
+1
View File
@@ -14,6 +14,7 @@ The Model Context Protocol (MCP) is an open standard for connecting AI agents to
| **API Key Authentication** | [`mcp_api_key_auth.py`](mcp_api_key_auth.py) | Demonstrates API key authentication with MCP servers using `header_provider`, runtime invocation kwargs, and a command-line API key argument |
| **GitHub Integration with PAT** | [`mcp_github_pat.py`](mcp_github_pat.py) | Demonstrates connecting to GitHub's MCP server using Personal Access Token (PAT) authentication |
| **Long-Running Task** | [`mcp_long_running_task.py`](mcp_long_running_task.py) | Demonstrates transparent SEP-2663 long-running task handling for MCP tools that advertise `taskSupport=required`. Self-spawns a stdio MCP child server |
| **Sampling Approval** | [`mcp_sampling_approval.py`](mcp_sampling_approval.py) | Demonstrates gating server-initiated `sampling/createMessage` requests with a `sampling_approval_callback`, plus the `sampling_max_tokens` and `sampling_max_requests` guardrails. MCP sampling is denied by default |
## Prerequisites