Question 1

What's the difference between GraphQL and REST?

Accepted Answer

REST: server defines endpoints, each returns a fixed shape (`/users/1` returns the user object). GraphQL: client requests exactly the fields it needs from a single endpoint (`{ user(id: 1) { name email } }`). GraphQL avoids over-fetching (REST endpoints often return more than you need) and under-fetching (REST often requires multiple roundtrips). Trade-off: query complexity, caching, and rate-limiting are harder than with REST.

Question 2

What is introspection and why is it useful?

Accepted Answer

GraphQL servers can describe their own schema via the special `__schema` and `__type` queries. The playground sends an introspection query to fetch the type system, then offers autocomplete, type checking, and schema browsing. Most public GraphQL APIs leave introspection on; some production servers disable it for security (hiding the schema from attackers), in which case you need the schema file from the team.

Question 3

How do I pass variables?

Accepted Answer

Define the variables in the query (`query MyQuery($id: ID!) { user(id: $id) { name } }`) and supply them as a JSON object in the variables panel (`{"id": "123"}`). Variables are typed and validated against the schema, which is safer than string-interpolating into the query. Always use variables for user input, string interpolation into GraphQL queries is the injection equivalent of SQL injection.

Question 4

What's a fragment?

Accepted Answer

A reusable named selection of fields: `fragment UserFields on User { id name email }`, then use `... UserFields` in queries. Fragments DRY up queries that share field sets and are essential for client libraries (Relay, Apollo) that use fragment colocation. The playground supports defining and using fragments in the query editor.

Question 5

How do mutations differ from queries?

Accepted Answer

Syntactically identical, semantically different. Queries are idempotent reads. Mutations modify server state, create, update, delete. GraphQL spec says: queries can execute in parallel; mutations execute serially within a single request. Convention: name mutations as verbs (`createUser`, `updatePost`); return updated data so clients can update their cache without a follow-up query.

Question 6

What about subscriptions?

Accepted Answer

Subscriptions are live streams over WebSocket or SSE, the server pushes updates when watched data changes. This playground typically handles HTTP queries/mutations only; for subscriptions you'd use a WebSocket-aware client. Common transport: `graphql-ws` protocol over WebSocket (the modern standard) or the older `subscriptions-transport-ws`.

Question 7

Why does my query return errors and data both?

Accepted Answer

GraphQL's response shape is `{ data: ..., errors: [...] }`. Partial success is possible, some fields succeeded, others failed. The HTTP status is usually 200 even with errors in the body. This is the most common GraphQL gotcha for REST-experienced devs: always check `errors`, not just HTTP status. Modern clients (Apollo, urql) surface this; raw fetch users must check explicitly.

Question 8

Is my query sent to your server?

Accepted Answer

The query is sent to YOUR GraphQL endpoint (the URL you supplied). The playground UI runs in your browser, but the HTTP request goes from your browser to your endpoint. The endpoint URL, headers (including auth tokens), query, variables, and response all stay between your browser and your server, they don't pass through ours.

Question 9

What standards does GraphQL Playground validate against?

Accepted Answer

GraphQL Playground checks compliance with Testing methodology specification.

Question 10

What are the limitations of GraphQL Playground?

Accepted Answer

Tests are client-side, does not test real server behavior Results may vary from production environment

Operation Type	Semantic Intent	Execution Pattern
Query	Read / Fetch Data	Parallel Execution (Idempotent)
Mutation	Write / State Change	Serial Execution (Non-Idempotent)
Subscription	Real-time Streaming	Persistent WebSocket / SSE Tunnel
Fragment	Reusable Selection	Selection set inlining across types

GraphQL Playground

Introspection

Response

Learn More

AES Interoperability Across 7 Libraries: We Encrypted the Same Plaintext Everywhere and Compared Results

cURL Cheatsheet for Developers 2026 — Every Flag You Actually Use

Essential API and Web Development Tools for Frontend and Backend Engineers

What is GraphQL Playground?

Frequently Asked Questions

Technical Deep Dive

GraphQL Playground

Real-Time Feedback

Edge-Case Coverage

Actionable Output

01 GQL Operation Architecture

02 Query Execution Pipeline

Runs 100% in your browser

You Might Also Need

API Response Diff

Email Address Validator

gRPC Web Tester

HTTP Request Headers Builder