> ## Documentation Index
> Fetch the complete documentation index at: https://gofastmcp.com/llms.txt
> Use this file to discover all available pages before exploring further.

# base

# `fastmcp.server.transforms.search.base`

Base class for search transforms.

Search transforms replace `list_tools()` output with a small set of
synthetic tools — a search tool and a call-tool proxy — so LLMs can
discover tools on demand instead of receiving the full catalog.

All concrete search transforms (`RegexSearchTransform`,
`BM25SearchTransform`, etc.) inherit from `BaseSearchTransform` and
implement `_make_search_tool()` and `_search()` to provide their
specific search strategy.

Example::

from fastmcp import FastMCP
from fastmcp.server.transforms.search import RegexSearchTransform

mcp = FastMCP("Server")

@mcp.tool
def add(a: int, b: int) -> int: ...

@mcp.tool
def multiply(x: float, y: float) -> float: ...

# Clients now see only `search_tools` and `call_tool`.

# The original tools are discoverable via search.

mcp.add\_transform(RegexSearchTransform())

## Functions

### `serialize_tools_for_output_json` <sup><a href="https://github.com/PrefectHQ/fastmcp/blob/main/src/fastmcp/server/transforms/search/base.py#L60" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>

```python  theme={"theme":{"light":"snazzy-light","dark":"dark-plus"}}
serialize_tools_for_output_json(tools: Sequence[Tool]) -> list[dict[str, Any]]
```

Serialize tools to the same dict format as `list_tools` output.

### `serialize_tools_for_output_markdown` <sup><a href="https://github.com/PrefectHQ/fastmcp/blob/main/src/fastmcp/server/transforms/search/base.py#L138" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>

```python  theme={"theme":{"light":"snazzy-light","dark":"dark-plus"}}
serialize_tools_for_output_markdown(tools: Sequence[Tool]) -> str
```

Serialize tools to compact markdown, using \~65-70% fewer tokens than JSON.

## Classes

### `BaseSearchTransform` <sup><a href="https://github.com/PrefectHQ/fastmcp/blob/main/src/fastmcp/server/transforms/search/base.py#L154" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>

Replace the tool listing with a search interface.

When this transform is active, `list_tools()` returns only:

* Any tools listed in `always_visible` (pinned).
* A **search tool** that finds tools matching a query.
* A **call\_tool** proxy that executes tools discovered via search.

Hidden tools remain callable — `get_tool()` delegates unknown
names downstream, so direct calls and the call-tool proxy both work.

Search results respect the full auth pipeline: middleware, visibility
transforms, and component-level auth checks all apply.

**Args:**

* `max_results`: Maximum number of tools returned per search.
* `always_visible`: Tool names that stay in the `list_tools`
  output alongside the synthetic search/call tools.
* `search_tool_name`: Name of the generated search tool.
* `call_tool_name`: Name of the generated call-tool proxy.

**Methods:**

#### `transform_tools` <sup><a href="https://github.com/PrefectHQ/fastmcp/blob/main/src/fastmcp/server/transforms/search/base.py#L199" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>

```python  theme={"theme":{"light":"snazzy-light","dark":"dark-plus"}}
transform_tools(self, tools: Sequence[Tool]) -> Sequence[Tool]
```

Replace the catalog with pinned + synthetic search/call tools.

#### `get_tool` <sup><a href="https://github.com/PrefectHQ/fastmcp/blob/main/src/fastmcp/server/transforms/search/base.py#L204" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>

```python  theme={"theme":{"light":"snazzy-light","dark":"dark-plus"}}
get_tool(self, name: str, call_next: GetToolNext) -> Tool | None
```

Intercept synthetic tool names; delegate everything else.