What does the Schema Validator do?

The Schema Validator checks your actor's actual dataset output against the schema you declared in your dataset_schema.json file, catching mismatches before they trigger maintenance flags on the Apify Store. It is one of the most important pre-deploy tools available to Apify developers because schema violations are the number one cause of actors being flagged for maintenance, which directly reduces your Store visibility and revenue. Here is what the Schema Validator checks for. Empty schemas — if your dataset_schema.json exists but defines no fields, the validator flags it immediately. Type mismatches — if your schema declares a field as a string but your actor outputs a number or array for that field, you get a detailed error showing the exact JSON path, the expected type, and the actual type. Undeclared fields — if your actor outputs fields that are not declared in your schema, these are flagged because they can cause issues for users who rely on the schema for data pipeline integration. Missing required fields — if your schema marks fields as required but your actor sometimes omits them, the validator catches this inconsistency. The validation process works by comparing a sample of your actor's actual output data against the declared schema, field by field and type by type. The output report lists every violation with enough detail to fix it immediately: the field path (e.g., results[0].price.currency), what the schema expected (string), and what the actor actually produced (null). This makes fixing schema issues straightforward rather than requiring you to manually diff JSON structures. To use the Schema Validator, run it locally before every push to your Apify actor repository. It executes in seconds and requires no API calls, so it is completely free. Integrate it into your development workflow as a pre-push check — many developers add it to a Git pre-push hook so schema violations are caught automatically before code reaches production. For related tools, see the questions about the Test Runner and Regression Tests, which provide additional pre-deploy validation. Visit apifyforge.com/tools/schema-validator for the full documentation and usage examples.