fastmcp-client-cli

Query and invoke tools on MCP servers using fastmcp list and fastmcp call. Use when you need to discover what tools a server offers, call tools, or integrate MCP servers into workflows.

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FastMCP CLI: List and Call

Use fastmcp list and fastmcp call to interact with any MCP server from the command line.

Listing Tools

# Remote server
fastmcp list http://localhost:8000/mcp

# Local Python file (runs via fastmcp run automatically)
fastmcp list server.py

# MCPConfig with multiple servers
fastmcp list mcp.json

# Stdio command (npx, uvx, etc.)
fastmcp list --command 'npx -y @modelcontextprotocol/server-github'

# Include full input/output schemas
fastmcp list server.py --input-schema --output-schema

# Machine-readable JSON
fastmcp list server.py --json

# Include resources and prompts
fastmcp list server.py --resources --prompts

Default output shows tool signatures and descriptions. Use --input-schema or --output-schema to include full JSON schemas, --json for structured output.

Calling Tools

# Key=value arguments (auto-coerced to correct types)
fastmcp call server.py greet name=World
fastmcp call server.py add a=3 b=4

# Single JSON object for complex/nested args
fastmcp call server.py create_item '{"name": "Widget", "tags": ["a", "b"]}'

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

# JSON output for scripting
fastmcp call server.py add a=3 b=4 --json

Type coercion is automatic: limit=5 becomes an integer, verbose=true becomes a boolean, based on the tool's input schema.

Server Targets

All commands accept the same server targets:

Target	Example
HTTP/HTTPS URL	`http://localhost:8000/mcp`
Python file	`server.py`
MCPConfig JSON	`mcp.json` (must have `mcpServers` key)
Stdio command	`--command 'npx -y @mcp/server'`
Discovered name	`weather` or `source:name`

Servers configured in editor configs (Claude Desktop, Claude Code, Cursor, Gemini CLI, Goose) or project-level mcp.json can be referenced by name. Use source:name (e.g. claude-code:my-server, cursor:weather) to target a specific source. Run fastmcp discover to see available names.

For SSE servers, pass --transport sse:

fastmcp list http://localhost:8000/mcp --transport sse

Auth

HTTP targets automatically use OAuth (no-ops if the server doesn't require auth). Disable with --auth none:

fastmcp call http://server/mcp tool --auth none

Discovering Configured Servers

# See all MCP servers in editor/project configs
fastmcp discover

# Filter by source
fastmcp discover --source claude-code

# JSON output
fastmcp discover --json

Scans Claude Desktop, Claude Code, Cursor, Gemini CLI, Goose, and ./mcp.json. Sources: claude-desktop, claude-code, cursor, gemini, goose, project.

Workflow Pattern

Discover tools first, then call them:

# 1. See what servers are configured
fastmcp discover

# 2. See what tools a server has
fastmcp list weather

# 3. Call a tool
fastmcp call weather get_forecast city=London

If you call a nonexistent tool, FastMCP suggests close matches.

Repository: PrefectHQ/fastmcp
Path: skills/fastmcp-client-cli/SKILL.md
Commit: c9cf237

Last updated: 2 days ago
First committed: 7 months ago

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