> ## Documentation Index

> Fetch the complete documentation index at: /llms.txt

> Use this file to discover all available pages before exploring further.

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CLI

# Client Commands

List tools, call them, and discover configured servers

New in version `3.0.0` The CLI can act as an MCP client — connecting to any server (local or remote) to list what it exposes and call its tools directly. This is useful for development, debugging, scripting, and giving shell-capable LLM agents access to MCP servers.

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Listing Tools

`fastmcp list` connects to a server and prints its tools as function signatures, showing parameter names, types, and descriptions at a glance:

    fastmcp list http://localhost:8000/mcp
    fastmcp list server.py
    fastmcp list weather  # name-based resolution

When you need the full JSON Schema for a tool’s inputs or outputs — for understanding nested objects, enum constraints, or complex types — opt in with `--input-schema` or `--output-schema`:

    fastmcp list server.py --input-schema

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Resources and Prompts

By default, only tools are shown. Add `--resources` or `--prompts` to include those:

    fastmcp list server.py --resources --prompts

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Machine-Readable Output

The `--json` flag switches to structured JSON with full schemas included. This is the format to use when feeding tool definitions to an LLM or building automation:

    fastmcp list server.py --json

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Options

Option | Flag | Description
--- | --- | ---
Command | `--command` | Connect via stdio (e.g., `'npx -y @mcp/server'`)
Transport | `--transport`, `-t` | Force `http` or `sse` for URL targets
Resources | `--resources` | Include resources in output
Prompts | `--prompts` | Include prompts in output
Input Schema | `--input-schema` | Show full input schemas
Output Schema | `--output-schema` | Show full output schemas
JSON | `--json` | Structured JSON output
Timeout | `--timeout` | Connection timeout in seconds
Auth | `--auth` | `oauth` (default for HTTP), a bearer token, or `none`

##
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Calling Tools

`fastmcp call` invokes a single tool on a server. Pass arguments as `key=value` pairs — the CLI fetches the tool’s schema and coerces your string values to the right types automatically:

    fastmcp call server.py greet name=World
    fastmcp call http://localhost:8000/mcp search query=hello limit=5

Type coercion is schema-driven: `"5"` becomes the integer `5` when the schema expects an integer. Booleans accept `true`/`false`, `yes`/`no`, and `1`/`0`. Arrays and objects are parsed as JSON.

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Complex Arguments

For tools with nested or structured parameters, `key=value` syntax gets awkward. Pass a single JSON object instead:

    fastmcp call server.py create_item '{"name": "Widget", "tags": ["sale"], "metadata": {"color": "blue"}}'

Or use `--input-json` to provide a base dictionary, then override individual keys with `key=value` pairs:

    fastmcp call server.py search --input-json '{"query": "hello", "limit": 5}' limit=10

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Error Handling

If you misspell a tool name, the CLI suggests corrections via fuzzy matching. Missing required arguments produce a clear message with the tool’s signature as a reminder. Tool execution errors are printed with a non-zero exit code, making the CLI straightforward to use in scripts.

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Structured Output

`--json` emits the raw result including content blocks, error status, and structured content:

    fastmcp call server.py get_weather city=London --json

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Interactive Elicitation

Some tools request additional input during execution through MCP’s elicitation mechanism. When this happens, the CLI prompts you in the terminal — showing each field’s name, type, and whether it’s required. You can type `decline` to skip a question or `cancel` to abort the call entirely.

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Options

Option | Flag | Description
--- | --- | ---
Command | `--command` | Connect via stdio
Transport | `--transport`, `-t` | Force `http` or `sse`
Input JSON | `--input-json` | Base arguments as JSON (merged with `key=value`)
JSON | `--json` | Raw JSON output
Timeout | `--timeout` | Connection timeout in seconds
Auth | `--auth` | `oauth`, a bearer token, or `none`

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Discovering Configured Servers

`fastmcp discover` scans your machine for MCP servers configured in editors and tools. It checks:

- Claude Desktop — `claude_desktop_config.json`
- Claude Code — `~/.claude.json`
- Cursor — `.cursor/mcp.json` (walks up from current directory)
- Gemini CLI — `~/.gemini/settings.json`
- Goose — `~/.config/goose/config.yaml`
- Project — `./mcp.json` in the current directory

    fastmcp discover

The output groups servers by source, showing each server’s name and transport. Filter by source or get machine-readable output:

    fastmcp discover --source claude-code
    fastmcp discover --source cursor --source gemini --json

Any server that appears here can be used by name with `list`, `call`, and other commands — so you can go from “I have a server in Claude Code” to querying it without copying URLs or paths.

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LLM Agent Integration

For LLM agents that can execute shell commands but don’t have native MCP support, the CLI provides a clean bridge. The agent calls `fastmcp list --json` to discover available tools with full schemas, then `fastmcp call --json` to invoke them with structured results. Because the CLI handles connection management, transport selection, and type coercion internally, the agent doesn’t need to understand MCP protocol details — it just reads JSON and constructs shell commands.

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Remote Stdio Bridges

For MCP hosts that expect a local stdio command but need to connect to a remote HTTP server, use `fastmcp-remote`. It provides a small standalone bridge for host configuration, while `fastmcp list` and `fastmcp call` remain focused on direct inspection and invocation from the terminal.
Inspecting Servers
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