The Contentful GraphQL API ships with GraphiQL by default. To get even better workflows (such as multiple tabs, speciyfing HTTP headers or work with multiple GraphQL APIs side-by-side), you can use a GraphQL Playground.
The endpoint of your Contentful GraphQL API has the following structure: https://cdn.contentful.com/spaces/{SPACE}/graphql/alpha/explore?access_token={CDA_TOKEN}
There are two placeholders that need to be replaced: