Collection of links to API resources: specifications, tutorials, or applications.
Be careful and do not use sensitive data in public web applications.
When learning, you need some APIs to play with. Most of the following APIs are available online and deployable solutions on your infrastructure.
BankGround: REST API, you can create user, account, and financial transactions in banking-like API. Easy to understand and practice REST skills.
Petstore: REST API, pet-store management API. It provides many operations with various HTTP methods and content types. Though, the API feedback (request validations, etc.) is limited.
Learn Web Services: two simple services (Hello and Celsius to Fahrenheit conversion) helpful in learning SOAP API basics.
BankGround: GraphQL API, you can practice both GraphQL queries and mutations. Create an account and transactions and try your queries.
Countries: provides information on continents, countries (name, code, capital, currency, etc.), and languages. Nice API to understand GraphQL queries.
OpenAPI Guide: a clear and precise guide on OpenAPI version 3 by Smartbear. Great reference and learning material.
OpenAPI Specification: less readable than OpenAPI Guide but sometimes good to go into detail.
GrapgQL.org: main GraphQL site. GraphQL tutorial, developer resources, and specifications.
Awesome API Security: A collection of awesome API Security tools and resources.
OpenAPI Tools: catalog of different tools to work with OpenAPI
Spectral Linter: linter to check OpenAPI definitions
XPath Tester: check XPath expressions on sample XML documents.
JSONPath Evaluator: evaluate JSONPath expression with sample JSON documents.