fastmcp/docs/python-sdk/fastmcp-experimental-transforms-code_mode.mdx
Jeremiah Lowin 3a9717e6be
Publish docs for v3.2.0 (#3713)
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Fix auto-close MRE script posting comment without closing (#3386)
Fix WorkOS token scope verification bypass 🤖 Generated with Codex (#3407)
Fix initialize McpError fallthrough 🤖 Generated with Codex (#3413)
Fix transform arg collisions with passthrough params (#3431)
Fix get_* returning None when latest version is disabled (#3439)
Fix get_* returning None when latest version is disabled (#3421)
Fix server lifespan overlap teardown (#3415)
Fix $ref output schema object detection regression (#3420)
resolved annotations (#3429)
Fix async partial callables rejected by iscoroutinefunction (#3438)
Fix async partial callables rejected by iscoroutinefunction (#3423)
fix: add version to components (#3458)
fix: use intent-based flag for OIDC scope patch in load_access_token (#3465)
Fixes #3461
fix: normalize Google scope shorthands and surface valid_scopes (#3477)
fix: resolve ty 0.0.23 type-checking errors and bump pin (#3481)
fix: shield lifespan teardown from cancellation (#3480)
fix: forward custom_route endpoints from mounted servers (#3462)
fix updates _get_additional_http_routes() to traverse providers,
Fixes #3457
fix: remove hardcoded version from CLI help text (#3456)
fix: monty 0.0.8 compatibility, drop external_functions from constructor (#3468)
fix: task test teardown hanging 5s per test (#3499)
Closes #3498
fix: validate workspace path is a directory before cursor install (#3440)
Fixes #3426
fix: handle re.error from malformed URI templates in build_regex (#3501)
fix: reject empty/OIDC-only required_scopes in AzureProvider (#3503)
fix: restrict $ref resolution to local refs only (SSRF/LFI) (#3502)
fix warnings and timeouts (#3504)
close upgrade check issue when build passes (#3505)
Closes #3484
fix: URL-encode path params to prevent SSRF/path traversal (GHSA-vv7q-7jx5-f767) (#3507)
fix: prevent path traversal in skill download (#3493)
fix: prefer IdP-granted scopes over client-requested scopes in OAuthProxy (#3492)
fix: remove unrelated transform and http.py changes from PR scope
fix: remove forced follow_redirects from httpx_client_factory calls (#3496)
fix: stop passing follow_redirects to httpx_client_factory
fix: restore follow_redirects=True for custom httpx client factories
Closes #3509
fix: CSRF double-submit cookie check in consent flow (#3519)
fix: validate server names in install commands (#3522)
fix: use raw strings for regex in pytest.raises match (#3523)
fix: reject refresh tokens used as Bearer access tokens (#3524)
fix: route ResourcesAsTools/PromptsAsTools through server middleware (#3495)
fix: resolve Pyright "Module is not callable" on @tool, @resource, @prompt decorators (#3540)
fix: filter warnings by message in KEY_PREFIX test (#3549)
fix: suppress output schema for ToolResult subclass annotations (#3548)
fix: increase sleep duration in proxy cache tests (#3567)
fix: store absolute token expiry to prevent stale expires_in on reload (#3572)
fix: preserve tool properties named 'title' during schema compression (#3582)
Fix loopback redirect URI port matching per RFC 8252 §7.3 (#3589)
Fix app tool routing: visibility check and middleware propagation (#3591)
Fix query parameter serialization to respect OpenAPI explode/style settings (#3595)
Fix dev apps form: union types, textarea support, JSON parsing (#3597)
fix(google): replace deprecated /oauth2/v1/tokeninfo with /oauth2/v3/userinfo (#3603)
fix: resolve EntraOBOToken dependency injection through MultiAuth (#3609)
fix(docs): correct misleading stateless_http header (#3622)
fix: filesystem provider import machinery (#3626)
Closes #3625 (issues 2, 3, 6)
fix: recover StdioTransport after subprocess exits (#3630)
fix(server): preserve mounted tool task metadata (#3632)
fix: scope deprecation warning filter to FastMCPDeprecationWarning (#3649)
fix imports, add PrefabAppConfig (#3650)
fix: resolve CurrentFastMCP/ctx.fastmcp to child server in mounted background tasks (#3651)
Fix blocking docs issues: chart imports, Select API, Rx consistency (#3652)
closed by default (#3657)
Fix prompt caching middleware missing wrap/unwrap round-trip (#3666)
fix: serialize object query params per OpenAPI style/explode rules (#3662)
Fixes #2857
fix: HTTP request headers not accessible in background task workers (#3631)
fix: restore HTTP headers in worker execution path for background tasks (#3681)
fix: strip discriminator after dereferencing schemas (#3682)
fix: remove stale ty:ignore directives for ty 0.0.26 (#3684)
Fix docs gaps in app provider pages (#3690)
fix: dev apps log panel UX improvements (#3698)
fix dev server empty string args (#3700)
2026-03-30 16:48:30 -04:00

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---
title: code_mode
sidebarTitle: code_mode
---
# `fastmcp.experimental.transforms.code_mode`
## Classes
### `SandboxProvider` <sup><a href="https://github.com/PrefectHQ/fastmcp/blob/main/src/fastmcp/experimental/transforms/code_mode.py#L73" 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#L82" 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#L91" 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#L109" 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#L179" 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#L261" 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#L322" 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#L389" 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#L438" 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#L488" 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#L491" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>
```python
get_tool(self, name: str, call_next: GetToolNext) -> Tool | None
```