ajv "must NOT have additional properties" in CI

By Kaveh Alemi·Latchkey

The schema sets additionalProperties: false, so ajv rejects any key it does not explicitly define. It reports "must NOT have additional properties" and names the extra property.

What this error means

ajv-cli fails with "must NOT have additional properties" and params.additionalProperty naming the offending key (often a typo of a valid one).

[
  {
    "instancePath": "",
    "schemaPath": "#/additionalProperties",
    "keyword": "additionalProperties",
    "params": { "additionalProperty": "versionn" },
    "message": "must NOT have additional properties"
  }
]

Common causes

A misspelled key not defined in the schema

A typo like versionn is not a declared property, and additionalProperties: false forbids unknown keys.

A new field the schema has not been updated for

The config added a legitimate field the schema does not yet list, so a strict schema rejects it.

How to fix it

Fix the typo or remove the stray key

1. Read params.additionalProperty to see the offending key.
2. Correct the spelling to a defined property, or delete the key.
3. Re-run ajv validate to confirm.

Add the property to the schema

If the field is valid, declare it under properties so the strict schema accepts it.

{
  "additionalProperties": false,
  "properties": {
    "name": { "type": "string" },
    "version": { "type": "string" }
  }
}

How to prevent it

• Keep additionalProperties: false to catch typos, and update the schema for real new fields.
• Validate in a pre-commit hook so unknown keys fail before merge.
• Review schema changes alongside config changes.

Frequently asked questions

Related guides

References

• GitHub Actions documentation