Using Schema Introspection
1. Understanding Introspection System
Field Returns __schema Whole schema metadata __type(name) Single type info __typename Concrete type at runtime
2. Querying Schema Types
Example: List all types
{ __schema { types { name kind description } queryType { name } mutationType { name } subscriptionType { name } } }
3. Querying Type Fields
Example: Inspect a type
{ __type ( name : "User" ) { name fields { name type { name kind ofType { name } } args { name type { name } defaultValue } isDeprecated deprecationReason } } }
{ __type ( name : "CreateUserInput" ) { inputFields { name type { name } defaultValue description } } }
5. Querying Enum Values
Example: Inspect enum
{ __type ( name : "Role" ) { enumValues ( includeDeprecated : false ) { name description isDeprecated deprecationReason } } }
6. Querying Interfaces
Example: Interfaces and implementers
{ __type ( name : "Node" ) { interfaces { name } possibleTypes { name } } }
7. Querying Possible Types
Use Detail Apollo cache possibleTypes config for fragment matching Codegen Generate discriminated unions Validation Verify spread compatibility
8. Disabling Introspection
Example: Disable in production
new ApolloServer ({ schema, introspection: process.env. NODE_ENV !== "production" });
Warning: Disabling introspection isn't real security — schema can still be reverse-engineered. Pair with persisted-query allowlists.
9. Using __typename Field
Where Returns Object/Interface/Union Concrete type name string Always queryable Even on abstract types Apollo cache Used as part of cache normalization key
10. Building Schema Documentation
Tool Output graphql-markdown Markdown docs SpectaQL Static HTML Magidoc Vue-based site GraphQL Inspector Schema diff + docs
11. Implementing Schema Diffing
Example: graphql-inspector diff
graphql-inspector diff main.graphql pr.graphql # Reports breaking, dangerous, non-breaking changes
Change Class Examples Breaking Field removed, type changed, arg required added Dangerous New nullable field, default change Safe New type, new optional arg