Debugging GraphQL is the process of identifying and resolving issues that occur during the execution of GraphQL queries and mutations. These issues may include incorrect data, missing or null fields, invalid query arguments, or resolver-level errors.

Magento 2 provides strong GraphQL support, and with the right tools and configuration, debugging GraphQL becomes straightforward and efficient.

Debugging GraphQL Queries Using PHPStorm and Xdebug

GraphQL requests in Magento are standard HTTP requests. This means you can debug them using Xdebug just like any other frontend or API request.

Starting an Xdebug Session via URL

You can trigger an Xdebug session by appending a query parameter to the GraphQL endpoint:

Starting an Xdebug Session via Cookie

Alternatively, you can start an Xdebug session by sending a cookie along with the request.

If PHPStorm is listening for incoming debug connections, Xdebug will attach and allow step-by-step execution using breakpoints.

Enabling GraphQL Debugging in Magento

Magento provides built-in GraphQL debugging capabilities that can be enabled from the environment configuration file.

Edit the app/etc/env.php file and add the following configuration:

Once enabled, Magento will include more detailed error information in GraphQL responses and store additional logs for execution tracking.

Steps to Debug GraphQL Queries

• Send the GraphQL Query
  Use tools like GraphiQL, GraphQL Playground, Postman, or frontend applications to execute the query or mutation.
• Inspect the GraphQL Response
  Check the errors section in the response for schema validation errors, missing fields, or resolver exceptions.
• Validate Queries Using GraphQL Explorer
  Use schema-aware tools to auto-generate queries and verify that fields and arguments are valid.
• Review Magento Logs
  Inspect files located in var/log and var/report for stack traces and GraphQL execution logs.
• Debug Resolver Classes
  Place breakpoints directly inside resolver classes (ResolverInterface::resolve) to inspect runtime data.

Common GraphQL Debugging Scenarios

• Fields returning null due to missing resolvers
• Incorrect argument definitions in schema.graphqls
• Authorization issues in custom resolvers
• Type mismatches between schema and returned data

Additional Debugging Best Practices

• Validate all queries against the GraphQL schema
• Split large or complex queries into smaller parts
• Use introspection to understand schema structure
• Carefully analyze GraphQL response payloads
• Compare query behavior across development and staging environments
• Refer to Magento community forums and GitHub issues when needed

Conclusion

Debugging GraphQL in Magento 2 requires a combination of proper tooling, configuration, and structured analysis. By enabling GraphQL debugging, leveraging Xdebug with PHPStorm, and inspecting resolvers directly, developers can quickly identify and fix issues in GraphQL queries.

Following best practices ensures faster development cycles, reliable APIs, and a smoother experience for frontend consumers using Magento GraphQL.