comfyui-mcp

call_tool

Execute a named ComfyUI tool with parameters in args and return the underlying tool's result.

Instructions

Execute a tool from the catalog by name. Pass its parameters in args (object). The result is exactly what the underlying tool returns.

Tool call template

This tool declares no required parameters. Add optional parameters from the input schema as needed.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {},
    "name": "call_tool"
  }
}

Input Schema

Name	Required	Description
`args`	No	The tool's parameters as an object matching its describe_tool schema. A JSON-encoded string is also accepted. Omit for tools without parameters.
`name`	No	Exact tool name from list_tools.
`arguments`	No	Alias for args.
`tool_name`	No	Alias for name.
`parameters`	No	Alias for args.

Schema Changelog

Changes observed during successful MCP inspections.

First observedv1.0.0Sep 30, 2026

TDQS

A3.8/5.0

Behavior3/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

No annotations are provided, so the description carries the burden. It states that the result is exactly what the underlying tool returns, which is a useful behavioral note. However, it doesn't disclose potential side effects, errors, or the dynamic nature of execution. The description is adequate but lacks depth.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness5/5

Is the description appropriately sized, front-loaded, and free of redundancy?

The description is two short sentences, front-loaded with the main purpose, and includes essential operational detail about parameter passing and return behavior. No wasted words.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness4/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

Given that the tool's behavior is dynamic (executing arbitrary tools), the description covers the essential invocation details: name, args, aliases, and the fact that the result is passthrough. The schema also documents aliases fully. While it doesn't mention error handling or edge cases (e.g., unknown tool), for a wrapper tool this is reasonably complete.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters3/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

The input schema has 100% coverage across the parameters, including descriptions for name, args, and aliases. The description adds a bit by explaining the args object matches the describe_tool schema, and a JSON string is accepted. This supplements the schema, but the schema already covers the semantics well, so baseline 3 is appropriate.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose4/5

Does the description clearly state what the tool does and how it differs from similar tools?

The description clearly states the tool's purpose: 'Execute a tool from the catalog by name' and how parameters are passed. It distinguishes itself from siblings like list_tools and describe_tool by focusing on execution, though it doesn't explicitly mention alternatives.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines4/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

The description gives clear context on when to use: when you need to execute a tool from the catalog, providing the tool name and parameters. It doesn't explicitly contrast with alternatives like list_tools or describe_tool, but the purpose is clear enough to differentiate.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.