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A webhook is an HTTP callback that one system sends to another to notify it of an event. Instead of the receiver polling for changes, the source POSTs an event payload to a URL the receiver registered ahead of time. Webhooks are the default integration mechanism between SaaS products.

How it works

The receiver registers a URL with the source (in a dashboard or via API). When an event occurs,…

An API Gateway is a server that sits in front of a collection of backend services and exposes a single entry point to clients. It typically handles request routing, authentication, rate limiting, request and response transformation, caching, and observability, so individual services can stay focused on business logic.

Common responsibilities

• Routing: map external paths to internal services
  …

Idempotency is the property that repeating an operation produces the same outcome as performing it once. An idempotent operation can be safely retried after a network failure, timeout, or partial failure, without risking duplicate side effects.

Idempotency by HTTP method

• GET, HEAD, OPTIONS: safe and idempotent by definition
• PUT, DELETE: idempotent (replacing or removing the same resource…

Pagination is the API pattern for splitting a large collection into smaller pages so clients fetch results incrementally. It is one of the universal API design decisions, with consequences for performance, consistency, and the client developer experience.

Common strategies

• Offset / page-number. ?page=3&limit=20. Simple, supports jumping to arbitrary pages, but slow on large tables and…

JSON (JavaScript Object Notation) is a lightweight, text-based data interchange format. It represents data as a small set of structures (objects, arrays, strings, numbers, booleans, null) that map naturally to native types in most programming languages, which is why it has become the default payload format for web APIs.

Structure

• Object: { "key": value } with string keys
• Array: [ value,…

OpenAPI (formerly Swagger) is a specification for describing HTTP APIs in a machine-readable format, typically YAML or JSON. An OpenAPI document defines an API's endpoints, request and response schemas, authentication, and examples, and is used to generate documentation, client SDKs, server stubs, and validation logic.

What it covers

• Paths and operations: URL templates with parameters,…

HATEOAS (Hypermedia As The Engine Of Application State) is the principle in Fielding's REST that responses must include links describing the next valid actions, so clients can navigate an application by following links rather than hard-coding URL structures.

How it works

A HATEOAS response returns not just data, but also a set of links (typically named relations such as self, next, edit,…

gRPC is a high-performance RPC framework developed at Google, using HTTP/2 as the transport and Protocol Buffers (protobuf) as the schema and serialization format. It is the default choice for internal service-to-service communication at many companies running microservices in compiled languages.

How it works

Services are defined in .proto files specifying messages and RPC methods. A code…

GraphQL is an API query language and runtime in which clients request exactly the fields they want from a typed schema. A single endpoint accepts queries, mutations, and subscriptions, and the server resolves only the requested fields, often combining data from multiple underlying sources.

How it works

The server publishes a schema written in the GraphQL SDL, defining types, queries,…

HTTP (Hypertext Transfer Protocol) is the application-layer protocol the web runs on. It defines how clients (typically browsers or API consumers) request resources from servers using methods like GET, POST, PUT, and DELETE, and how servers respond with status codes, headers, and an optional body.

How it works

HTTP is a request-response protocol over a reliable transport, traditionally TCP. A…

Spring Boot is the most widely used Java framework for building production server applications. Built on top of the broader Spring Framework, Spring Boot adds auto-configuration, an embedded application server, and a "starter" dependency system so developers can launch a working web application in minutes instead of wiring XML configuration by hand.

Core pieces

• Auto-configuration. Spring…

Ruby on Rails (or just Rails) is a server-side web framework written in Ruby and released in 2004. Rails popularised the "convention over configuration" philosophy, the MVC pattern in web frameworks, and the idea that one developer could build a complete production application in days. GitHub, Shopify, Basecamp, and many SaaS products are built on Rails.

Core pieces

• Active Record. The ORM…