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

# 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 theme={"theme":{"light":"snazzy-light","dark":"dark-plus"}}
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.