GraphQL Schema Validator — Type Error Detector
Validate GraphQL SDL schema syntax and detect type conflicts or missing definitions. Paste your schema to instantly check for duplicate type names, undefined type references, unclosed braces, and empty type bodies. Errors are shown with line numbers and actionable fix suggestions. All validation runs in your browser — your schema is never sent anywhere.
How to Use GraphQL Schema Validator — Type Error Detector
How to Use the GraphQL Schema Validator
Step 1: Paste Your Schema
Paste your GraphQL Schema Definition Language (SDL) into the textarea. This can be a complete schema or a partial type definition you are working on. The validator analyzes the text in real-time as you type.
Step 2: Load an Example (optional)
Click one of the example buttons to load a pre-built schema:
- Blog API (valid) — a complete blog schema with Query, Mutation, types, input, and enum
- Auth API (valid) — a login/register schema with JWT payload and roles
- With Errors — intentionally broken schema demonstrating common mistakes
Step 3: Read the Status
The status card shows whether the schema is valid (green check) or invalid (red X). Below it, four metric cards show the total number of types defined, total fields, error count, and warning count.
Step 4: Review Issues
If errors or warnings exist, the Issues panel lists each one with:
- Line number — the line in your schema where the problem was found
- Description — what the error or warning is
- Fix suggestion — a specific action to resolve it
Errors (red) prevent the schema from being valid. Warnings (amber) are non-blocking but indicate potential problems such as empty type bodies.
Step 5: Check the Type Breakdown
The Defined Types panel lists every type, interface, enum, union, input, and scalar found in the schema, along with their kind badge and field count. This gives you a quick overview of your schema structure.
Checks Performed
- Brace balance — detects unclosed or extra closing braces
- Duplicate type names — flags any type defined more than once
- Undefined type references — flags types used in fields that are not defined in the schema or as a built-in scalar (String, Int, Float, Boolean, ID)
- Empty type bodies — warns when a type, interface, input, or enum has no fields
Limitations
This is a lightweight heuristic validator, not a full GraphQL parser. It validates single-line formatted schemas (each field on its own line). It does not check argument types, directive definitions, schema extensions, or fragment spreads. For full spec compliance, use an official GraphQL library in your build pipeline.
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