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:
  • the first element is the string node ID of the source node
  • the second element is the integer index into the source node's output list (0-based)
• _meta is optional and 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