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docs/python-sdk/fastmcp-experimental-transforms-code_mode.mdx

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fastmcp.experimental.transforms.code_mode

Classes

SandboxProvider <sup><a href="https://github.com/PrefectHQ/fastmcp/blob/main/src/fastmcp/experimental/transforms/code_mode.py#L76" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>

Interface for executing LLM-generated Python code in a sandbox.

WARNING: The code parameter passed to run contains untrusted, LLM-generated Python. Implementations MUST execute it in an isolated sandbox — never with plain exec(). Use MontySandboxProvider (backed by pydantic-monty) for production workloads.

Methods:

run <sup><a href="https://github.com/PrefectHQ/fastmcp/blob/main/src/fastmcp/experimental/transforms/code_mode.py#L85" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>

python
run(self, code: str) -> Any

MontySandboxProvider <sup><a href="https://github.com/PrefectHQ/fastmcp/blob/main/src/fastmcp/experimental/transforms/code_mode.py#L94" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>

Sandbox provider backed by pydantic-monty.

Args:

  • limits: Resource limits for sandbox execution. Supported keys: max_duration_secs (float), max_allocations (int), max_memory (int), max_recursion_depth (int), gc_interval (int). All are optional; omit a key to leave that limit uncapped.

Methods:

run <sup><a href="https://github.com/PrefectHQ/fastmcp/blob/main/src/fastmcp/experimental/transforms/code_mode.py#L112" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>

python
run(self, code: str) -> Any

Search <sup><a href="https://github.com/PrefectHQ/fastmcp/blob/main/src/fastmcp/experimental/transforms/code_mode.py#L178" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>

Discovery tool factory that searches the catalog by query.

Args:

  • search_fn: Async callable (tools, query) -> matching_tools. Defaults to BM25 ranking.
  • name: Name of the synthetic tool exposed to the LLM.
  • default_detail: Default detail level for search results. "brief" returns tool names and descriptions only. "detailed" returns compact markdown with parameter schemas. "full" returns complete JSON tool definitions.
  • default_limit: Maximum number of results to return. The LLM can override this per call. None means no limit.

GetSchemas <sup><a href="https://github.com/PrefectHQ/fastmcp/blob/main/src/fastmcp/experimental/transforms/code_mode.py#L260" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>

Discovery tool factory that returns schemas for tools by name.

Args:

  • name: Name of the synthetic tool exposed to the LLM.
  • default_detail: Default detail level for schema results. "brief" returns tool names and descriptions only. "detailed" renders compact markdown with parameter names, types, and required markers. "full" returns the complete JSON schema.

GetTags <sup><a href="https://github.com/PrefectHQ/fastmcp/blob/main/src/fastmcp/experimental/transforms/code_mode.py#L321" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>

Discovery tool factory that lists tool tags from the catalog.

Reads tool.tags from the catalog and groups tools by tag. Tools without tags appear under "untagged".

Args:

  • name: Name of the synthetic tool exposed to the LLM.
  • default_detail: Default detail level. "brief" returns tag names with tool counts. "full" lists all tools under each tag.

ListTools <sup><a href="https://github.com/PrefectHQ/fastmcp/blob/main/src/fastmcp/experimental/transforms/code_mode.py#L388" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>

Discovery tool factory that lists all tools in the catalog.

Args:

  • name: Name of the synthetic tool exposed to the LLM.
  • default_detail: Default detail level. "brief" returns tool names and one-line descriptions. "detailed" returns compact markdown with parameter schemas. "full" returns the complete JSON schema.

CodeMode <sup><a href="https://github.com/PrefectHQ/fastmcp/blob/main/src/fastmcp/experimental/transforms/code_mode.py#L437" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>

Transform that collapses all tools into discovery + execute meta-tools.

Discovery tools are composable via the discovery_tools parameter. Each is a callable that receives catalog access and returns a Tool. By default, Search and GetSchemas are included for progressive disclosure: search finds candidates, get_schema retrieves parameter details, and execute runs code.

The execute tool is always present and provides a sandboxed Python environment with call_tool(name, params) in scope.

Methods:

transform_tools <sup><a href="https://github.com/PrefectHQ/fastmcp/blob/main/src/fastmcp/experimental/transforms/code_mode.py#L487" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>

python
transform_tools(self, tools: Sequence[Tool]) -> Sequence[Tool]

get_tool <sup><a href="https://github.com/PrefectHQ/fastmcp/blob/main/src/fastmcp/experimental/transforms/code_mode.py#L490" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>

python
get_tool(self, name: str, call_next: GetToolNext) -> Tool | None