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fastmcp.cli.client

Client-side CLI commands for querying and invoking MCP servers.

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Functions

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resolve_server_spec 

resolve_server_spec(server_spec: str | None) -> str | dict[str, Any] | ClientTransport
Turn CLI inputs into something Client() accepts. Exactly one of server_spec or command should be provided. Resolution order for server_spec:
  1. URLs (http://, https://) — passed through as-is. If --transport is sse, the URL is rewritten to end with /sse so infer_transport picks the right transport.
  2. Existing file paths, or strings ending in .py/.js/.json.
  3. Anything else — name-based resolution via resolve_name.
When command is provided, the string is shell-split into a StdioTransport(command, args).

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coerce_value 

coerce_value(raw: str, schema: dict[str, Any]) -> Any
Coerce a string CLI value according to a JSON-Schema type hint.

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parse_tool_arguments 

parse_tool_arguments(raw_args: tuple[str, ...], input_json: str | None, input_schema: dict[str, Any]) -> dict[str, Any]
Build a tool-call argument dict from CLI inputs. A single JSON object argument is treated as the full argument dict. --input-json provides the base dict; key=value pairs override. Values are coerced using the tool’s inputSchema.

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format_tool_signature 

format_tool_signature(tool: mcp.types.Tool) -> str
Build name(param: type, ...) -> return_type from a tool’s JSON schemas.

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list_command 

list_command(server_spec: Annotated[str | None, cyclopts.Parameter(help='Server URL, Python file, MCPConfig JSON, or .js file')] = None) -> None
List tools available on an MCP server. Examples: fastmcp list http://localhost:8000/mcp fastmcp list server.py fastmcp list mcp.json —json fastmcp list —command ‘npx -y @mcp/server’ —resources fastmcp list http://server/mcp —transport sse

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call_command 

call_command(server_spec: Annotated[str | None, cyclopts.Parameter(help='Server URL, Python file, MCPConfig JSON, or .js file')] = None, target: Annotated[str, cyclopts.Parameter(help='Tool name, resource URI, or prompt name (with --prompt)')] = '', *arguments: str) -> None
Call a tool, read a resource, or get a prompt on an MCP server. By default the target is treated as a tool name. If the target contains :// it is treated as a resource URI. Pass --prompt to treat it as a prompt name. Arguments are passed as key=value pairs. Use —input-json for complex or nested arguments. Examples: 
fastmcp call server.py greet name=World
fastmcp call server.py resource://docs/readme
fastmcp call server.py analyze --prompt data='[1,2,3]'
fastmcp call http://server/mcp create --input-json '{"tags": ["a","b"]}'

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discover_command 

discover_command() -> None
Discover MCP servers configured in editor and project configs. Scans Claude Desktop, Claude Code, Cursor, Gemini CLI, Goose, and project-level mcp.json files for MCP server definitions. Discovered server names can be used directly with fastmcp list and fastmcp call instead of specifying a URL or file path. Examples: fastmcp discover fastmcp discover —source claude-code fastmcp discover —source cursor —source gemini —json fastmcp list weather fastmcp call cursor:weather get_forecast city=London