Required input is missing: identify the exact node and field

Symptoms and scope

The backend found a missing required input before execution. Use the reported node and field to repair that specific gap before investigating further failures.

Error fragments for search; IDs, values and filenames may vary:

Required input is missing
required_input_missing

Source-supported context

Core validate_inputs checks the presence of inputs declared required by the current node. The /prompt response's node_errors is more precise than a generic execution-failed banner. Source 1 Source 2

Cases to distinguish

1. A required socket is disconnected or a widget value was not exported.

2. An API client omitted a field, used the wrong inputs nesting or removed a meaningful value.

3. A node update added a required input that an older workflow has not supplied.

Diagnostic sequence

The sequence below is an editorial procedure based on the cited context, not a diagnosis already confirmed for your environment.

Step 1. Expand the error details and record the node ID, technical class and input_name.

Step 2. Inspect the current node UI or server /object_info to distinguish required and optional definitions.

Step 3. Connect an upstream output of the correct type or provide the defined literal value. Adding a same-named null is not necessarily valid.

Step 4. Re-export and inspect the actual request inputs before resubmitting. Document the template migration when an update introduced the field.

Completion check

The missing-input error disappears and the related upstream nodes also validate. Other genuine errors may become visible afterwards.

Limitations and cautions

Identical input names on different nodes can have different meanings. Do not insert arbitrary images, models or fictional paths just to satisfy presence checks.

Original sources

• ComfyUI execution.py validation — original record checked 2026-09-21.
• ComfyUI Server API routes — original record checked 2026-09-21.

Localization prepared: 2026-09-22. The source-check dates above were inherited from the existing article; this translation does not claim they were all rechecked today. No GPU run, minimum-memory measurement or runtime guarantee is supplied.

Related troubleshooting and guides

• Return type mismatch: inspect the source output slot and destination input
• POST /prompt returns 400: inspect node_errors before retrying