Comfyui Core

ComfyUI Core Knowledge

Workflow JSON Format (API Format)

ComfyUI workflows are JSON objects mapping string node IDs to node definitions:

{
  "1": {
    "class_type": "CheckpointLoaderSimple",
    "inputs": { "ckpt_name": "sd_xl_base_1.0.safetensors" },
    "_meta": { "title": "Load Checkpoint" }
  },
  "2": {
    "class_type": "CLIPTextEncode",
    "inputs": { "text": "a cat", "clip": ["1", 1] },
    "_meta": { "title": "Positive Prompt" }
  }
}

Key Rules

• Node IDs are strings of integers ("1", "2", etc.)
• class_type is the exact Python class name of the node
• inputs contains both widget values (scalars) and connections (arrays)
• Connections use the format ["sourceNodeId", outputIndex] — a 2-element array where:
• First element: string node ID of the source node
• Second element: integer index into the source node's output list (0-based)
• _meta is optional, used for display titles only

Connection Examples

"model": ["1", 0]       // Connect to node 1's first output (MODEL)
"clip": ["1", 1]        // Connect to node 1's second output (CLIP)
"vae": ["1", 2]         // Connect to node 1's third output (VAE)
"positive": ["2", 0]    // Connect to node 2's first output (CONDITIONING)
"samples": ["5", 0]     // Connect to node 5's first output (LATENT)
"images": ["6", 0]      // Connect to node 6's first output (IMAGE)

Important: API Format vs Web UI Format

• API format (what we use): { "1": { class_type, inputs }, "2": { ... } }
• Web UI format (saved workflows): { "nodes": [...], "links": [...] } — includes layout positions, visual metadata
• All MCP tools expect and return API format
• get_workflow defaults to format="api" which auto-converts saved UI-format workflows to compact API format
• Muted/bypassed nodes are preserved with _meta.mode: "muted" — these are inactive but visible for understanding the workflow
• Get/Set virtual wire nodes are preserved with _meta.title and Constant key for tracing data flow

Workflow Library Tools

• analyze_workflow(filename) — use this first to understand any saved workflow. Returns a structured text summary with sections, node IDs, key settings, virtual wires, and connection graph. No raw JSON — just what you need to reason about the workflow. Supports views: summary (default), overview (mermaid), detail (section mermaid), list, flat.
• list_workflows — list all saved workflows in ComfyUI's user library
• get_workflow(filename) — load raw workflow JSON. Only use when you need the actual JSON for enqueue_workflow, modify_workflow, or save_workflow. Use analyze_workflow instead for understanding.
• save_workflow(filename, workflow) — save a workflow to the user library

Data Types

ComfyUI nodes pass typed data through connections:

| Type | Description | Common Source | |------|-------------|---------------| | MODEL | Diffusion model weights | CheckpointLoaderSimple (output 0) | | CLIP | Text encoder | CheckpointLoaderSimple (output 1) | | VAE | Variational autoencoder | CheckpointLoaderSimple (output 2) | | CONDITIONING | Encoded text prompt | CLIPTextEncode (output 0) | | LATENT | Latent space tensor | EmptyLatentImage, KSampler, VAEEncode | | IMAGE | Pixel image tensor (BHWC) | VAEDecode, LoadImage, SaveImage | | MASK | Single-channel mask | LoadImage (output 1) | | UPSCALE_MODEL | Upscaling model | UpscaleModelLoader |

Standard Pipeline Patterns

Text-to-Image (txt2img)

CheckpointLoaderSimple → MODEL, CLIP, VAE
  ├─ CLIP → CLIPTextEncode (positive) → CONDITIONING
  ├─ CLIP → CLIPTextEncode (negative) → CONDITIONING
  │
EmptyLatentImage → LATENT
  │
KSampler (model, positive, negative, latent_image) → LATENT
  │
VAEDecode (samples, vae) → IMAGE
  │
SaveImage (images)

Node IDs typically: 1=Checkpoint, 2=Positive, 3=Negative, 4=EmptyLatent, 5=KSampler, 6=VAEDecode, 7=SaveImage

Image-to-Image (img2img)

Same as txt2img but replace EmptyLatentImage with:

LoadImage → IMAGE
VAEEncode (pixels, vae) → LATENT → KSampler.latent_image

Set KSampler.denoise to 0.5–0.8 (lower = closer to input image).

Upscale

LoadImage → IMAGE
UpscaleModelLoader → UPSCALE_MODEL
ImageUpscaleWithModel (upscale_model, image) → IMAGE
SaveImage (images)

Inpaint

LoadImage (image) → IMAGE → VAEEncode → LATENT
LoadImage (mask) → MASK
SetLatentNoiseMask (samples, mask) → LATENT → KSampler.latent_image

MCP Tool Usage Guide

Quick Generation

1. create_workflow with template "txt2img" and your params
2. enqueue_workflow with the returned JSON — returns prompt_id immediately
3. Poll get_job_status with the prompt_id until done is true
4. Use list_output_images (limit 1) to find the generated image, then Read to display it

Inspect & Modify

• get_node_info — query what nodes are available and their schemas
• modify_workflow — patch an existing workflow (setinput, addnode, removenode, connect, insertbetween)
• visualize_workflow — see a workflow as a mermaid diagram

Reverse Engineering

• visualize_workflow — workflow JSON → mermaid diagram
• mermaid_to_workflow — mermaid diagram → workflow JSON (uses /object_info for schema resolution)

Model Management

• list_local_models — see what's installed
• search_models — find models on HuggingFace
• download_model — download to ComfyUI's models directory

Important: Never ask the user to manually download models. If a required model is missing, proactively search for it and download it yourself:

1. Check list_local_models first
2. If missing, search HuggingFace via search_models or CivitAI via their REST API
3. Use download_model to install it directly to the correct subfolder

CivitAI API (when CIVITAI_API_TOKEN env var is available):

• Search: GET https://civitai.com/api/v1/models?query={query}&types=Checkpoint&sort=Most+Downloaded&limit=5
• Details: GET https://civitai.com/api/v1/models/{modelId}
• Download: GET https://civitai.com/api/download/models/{modelVersionId}?token={token}

CivitAI is preferred for fine-tuned models, community-rated checkpoints, and specialized LoRAs. HuggingFace is preferred for official/base models (SDXL, Flux, SD 1.5).

Custom Nodes

• search_custom_nodes — search the ComfyUI Registry
• get_node_pack_details — get details about a specific pack
• generate_node_skill — auto-generate a skill file for a node pack

Workflow Execution

enqueue_workflow submits to ComfyUI's queue and returns prompt_id + queue position immediately. It does NOT block.

Background Progress Monitoring

After enqueuing one or more workflows, use a background Bash task to monitor progress silently:

# Single job
Bash(run_in_background: true):
node "${CLAUDE_PLUGIN_ROOT}/scripts/monitor-progress.mjs" 

# Multiple jobs (batch)
Bash(run_in_background: true):
node "${CLAUDE_PLUGIN_ROOT}/scripts/monitor-progress.mjs"   

The script connects to ComfyUI's WebSocket and reports:

• Step-by-step progress (e.g., KSampler step 12/20 (60%))
• Success with output filenames and timing
• Errors with node details and messages

Standard generation pattern:

1. create_workflow or build workflow JSON + enqueue_workflow (repeat for batch)
2. Start background monitor with all prompt_ids
3. Continue conversation — results appear when jobs finish
4. Use list_output_images or Read to display the generated images

Do NOT poll get_job_status in a loop. The background monitor replaces polling entirely.

Fallback: If the monitor script is unavailable, use get_job_status to poll until done is true.

Queue Management

• get_queue — shows running/pending job counts and prompt_ids
• get_job_status — check if a specific prompt_id is running, pending, or done
• cancel_job — interrupt a running job (pass optional prompt_id to target a specific one)
• cancel_queued_job — remove a specific pending job from the queue by prompt_id
• clear_queue — remove all pending jobs (does NOT stop the currently running job)

When to use queue tools:

• To check status: get_job_status for a quick boolean check (prefer background monitor for ongoing tracking)
• To abort: cancel_job stops what's running now; cancel_queued_job removes a pending one
• To start fresh: clear_queue then optionally cancel_job

Monitoring & Recovery

• get_system_stats — GPU, VRAM, Python version, OS details
• get_queue — see running/pending jobs (also listed above under Queue Management)

When ComfyUI is unresponsive or crashed:

1. Try get_system_stats — if it fails, ComfyUI is down
2. Use restart_comfyui to restart it (preserves launch args from prior stop_comfyui)
3. If restart fails (no saved process info), use start_comfyui or ask the user to start it manually
4. After ComfyUI is back, re-enqueue any failed/lost workflows

When a job appears hung (monitor shows [STALL]):

1. Check get_system_stats — look at VRAM usage (OOM causes hangs)
2. Try cancel_job to interrupt the stuck job
3. If cancel fails, use restart_comfyui to force-restart
4. Use clear_vram after restart to free GPU memory before retrying

KSampler Parameters

| Parameter | Type | Common Values | |-----------|------|---------------| | seed | int | Random (0 to 2^48). Omit to auto-randomize. | | steps | int | 20 (standard), 4-8 (turbo/lightning models) | | cfg | float | 7-8 (SD 1.5/SDXL), 1.0 (Flux), 3.5 (turbo) | | sampler_name | string | "euler", "euler_ancestral", "dpmpp_2m", "dpmpp_sde" | | scheduler | string | "normal", "karras", "sgm_uniform" | | denoise | float | 1.0 (txt2img), 0.5-0.8 (img2img), 0.75-0.9 (inpaint) |

Mermaid Visualization Conventions

The visualize_workflow tool produces mermaid flowcharts with:

• Subgraphs grouping nodes by category: loading, conditioning, sampling, image, output
• Edge labels showing data types: -->|MODEL|, -->|CLIP|, -->|LATENT|, etc.
• Node labels showing class_type and optionally widget values
• Direction: LR (left-to-right) by default, TB (top-to-bottom) for large workflows

The mermaid_to_workflow tool parses mermaid back into workflow JSON, using connection type labels to resolve the correct input/output slots via /object_info schemas.

Common Mistakes to Avoid

1. Wrong connection format: Use ["1", 0] not [1, 0] — node IDs are strings
2. Web UI format: Don't pass { nodes: [], links: [] } — use API format
3. Missing VAE: CheckpointLoaderSimple has 3 outputs — MODEL(0), CLIP(1), VAE(2)
4. Wrong output index: Check the node's output list order via get_node_info
5. Seed handling: enqueue_workflow randomizes seeds by default unless disable_random_seed: true

Source & license

This open-source skill is cataloged on AgentStack and links to its original source — we do not rehost the code.

• Author: artokun
• Source: artokun/comfyui-mcp
• License: MIT
• Homepage: https://comfyui-mcp.artokun.io/docs

Install and usage instructions live in the source repository linked above.