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IO-AtelierTech

ComfyUI MCP Server

by IO-AtelierTech
OverviewSchemaRelated ServersScoreDiscussions
Python
Hybrid

list_extensions

Lists installed ComfyUI custom node extensions to verify available functionality for workflow automation.

Instructions

List loaded ComfyUI extensions.

Returns list of installed extension names (custom node packs). Use this to verify which custom nodes are available (e.g., fal.ai connector).

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault

No arguments

Implementation Reference

  • src/comfy_mcp_server/tools/discovery.py:146-158 (handler)
    The @mcp.tool()-decorated handler function that implements the 'list_extensions' tool. It fetches the list of loaded ComfyUI extensions from the '/extensions' API endpoint, logs progress if context provided, and returns error list on failure.
    @mcp.tool()
def list_extensions(ctx: Context = None) -> list:
    """List loaded ComfyUI extensions.

    Returns list of installed extension names (custom node packs).
    Use this to verify which custom nodes are available (e.g., fal.ai connector).
    """
    if ctx:
        ctx.info("Listing extensions...")
    try:
        return comfy_get("/extensions")
    except Exception as e:
        return [f"Error: {e}"]

Tool Definition Quality

A4.2/5.0
Behavior3/5

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

No annotations are provided, so the description carries the full burden. It discloses that the tool returns a list of installed extension names, which is useful behavioral context. However, it lacks details on potential limitations (e.g., whether it includes built-in vs. third-party extensions, error handling, or performance characteristics).

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 highly concise and well-structured: three brief sentences that each add value—stating the action, describing the return value, and providing usage context. There is no redundant or verbose language, and information is front-loaded effectively.

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 the tool's simplicity (0 parameters, no annotations, no output schema), the description is largely complete: it explains what the tool does and its purpose. However, without an output schema, it could benefit from more detail on the return format (e.g., list structure, data types) to fully guide the agent.

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

Parameters4/5

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

The input schema has 0 parameters with 100% coverage, so no parameter documentation is needed. The description appropriately does not discuss parameters, focusing instead on the tool's purpose and output. A baseline of 4 is applied as it correctly omits unnecessary parameter details.

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

Purpose5/5

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

The description clearly states the specific action ('List loaded ComfyUI extensions') and resource ('extensions'), distinguishing it from siblings like list_models or list_nodes by focusing on extension names/custom node packs. It provides a concrete example ('fal.ai connector') to illustrate the resource type.

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 explicitly states when to use this tool: 'to verify which custom nodes are available.' This provides clear context for its purpose. However, it does not mention when not to use it or name specific alternatives among siblings (e.g., list_nodes for node details vs. list_extensions for extension packs).

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

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