---
title: completions
sidebarTitle: completions
---

# `fastmcp.server.completions`


Server-side argument completion for FastMCP.

A completion request names a reference — a specific prompt or resource
template — and the argument being completed, plus a context of the argument
values already supplied. The server answers with candidate string values.

FastMCP surfaces this as a single server-level handler registered with
``@mcp.completion``, mirroring the MCP SDK's own ``completion/complete`` shape
and FastMCP's client-side ``Client.complete()``. The handler receives the
reference, the argument, and the optional context, and returns candidates for
whichever reference/argument pair it recognizes.


## Functions

### `normalize_completion` <sup><a href="https://github.com/PrefectHQ/fastmcp/blob/main/fastmcp_slim/fastmcp/server/completions.py#L54" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>

```python
normalize_completion(result: CompletionValues) -> mcp_types.Completion
```


Coerce a handler's return value into a wire ``Completion``.

A returned ``str`` is rejected: it is almost always a mistake (the value
would iterate into one-character candidates), so it raises rather than
silently producing surprising output.

The MCP contract caps a completion at 100 values, so a longer result is
truncated to the first 100 with ``has_more`` set — a handler that returns
thousands of matches emits a conforming response rather than an oversized
one that strict clients reject.

