What is the difference between rest and API?

General Communication vs Architectural Style

Understanding the difference between rest and api helps developers choose the correct architecture for software communication. Recognizing these fundamental distinctions prevents integration errors and improves backend system design efficiency.

Understanding the Core Relationship: What is an API vs. What is REST?

At its heart, an API (Application Programming Interface) is a broad software contract that allows different applications to talk to each other. REST, on the other hand, is a specific architectural style rather than a standalone technology.

Most developers - and I remember making this exact mistake when I first started building web services - confuse the two because they frequently see them written together as REST API. But think of a general API as a vehicle category, while a REST API is a specific type of car engineered for the web.

The Vehicle Analogy: Broad Interfaces vs. Specific Rules

An API can be built using almost any protocol, including TCP sockets, custom binary formats, or older SOAP standards. It is simply the gateway through which systems exchange requests and responses.

REST places strict boundaries on that exchange. It requires standard HTTP methods, stateless communication, and a uniform resource interface. Industry data shows that 83 percent of public web services rely on REST due to its standardized predictability.

How General APIs Function Behind the Scenes

A general API acts as an intermediary layer, exposing functions or data endpoints without forcing developers to adhere to rigorous architectural constraints. You can build an API using remote procedure calls, message queues, or streaming protocols.

This flexibility comes with a trade-off. Without a shared architectural style, clients and servers become tightly coupled. If the underlying data schema changes, client applications often break, requiring extensive refactoring across teams.

When General APIs Outshine REST

Sometimes strict REST constraints slow down high-performance internal systems. Real-time streaming applications, for example, often use WebSockets or gRPC rather than standard REST endpoints because persistent bidirectional channels eliminate HTTP overhead.

The Six Architectural Constraints of REST APIs

To earn the title of a true RESTful API, a service must incorporate six guiding constraints established during the early evolution of the web. These rules dictate how data is requested, processed, and cached.

Statelessness is perhaps the most critical constraint. Each request from a client must contain all necessary authentication and context data, allowing any server in a cluster to handle the request independently.

Cacheability and Layered Systems

Because REST utilizes standard HTTP headers, responses can be explicitly marked as cacheable or non-cacheable. This feature reduces unnecessary server trips and improves throughput. Industry benchmarks indicate that properly configured caching cuts redundant database queries by up to 60 percent in high-traffic applications.

Furthermore, REST supports a layered architecture. Clients cannot tell whether they are communicating directly with an origin server or an intermediary proxy, which improves system security and load balancing scalability.

Key Structural and Operational Differences

Evaluating the difference between web api and rest api comes down to examining design flexibility versus architectural discipline.

Here is the critical distinction: a general API can be messy, combining verbs and nouns arbitrarily in endpoint URLs like /getUserData?id=5. A REST API enforces resource-based modeling, using nouns and standard HTTP verbs to create predictable routes like GET /users/5.

Comparing General APIs and REST APIs

General API (Web API)

• Can maintain session state on the server or use stateful connection channels

• Flexible and unconstrained; can use any protocol, data format, or custom RPC pattern

• Often mixes verbs and RPC-style action names in URLs (e.g., /getAccountDetails)

• Real-time streaming, legacy enterprise integrations, or custom internal microservices

REST API ⭐ (Recommended)

• Completely stateless; every request contains all required information

• Strict adherence to six constraints including statelessness and uniform interface

• Resource-oriented modeling using standard HTTP methods (GET, POST, PUT, DELETE)

• Public web services, mobile app backends, and standard CRUD operations

Startup API Redesign Journey

DevFlow, a SaaS startup serving 12,000 active users, initially built an ad-hoc custom API using RPC methods and non-standard endpoints. As the engineering team expanded, new developers struggled to understand undocumented endpoint conventions, leading to frequent integration bugs.

First attempt: They tried patching the existing custom API by adding more custom parameters. Result: Response times degraded and client apps crashed whenever backend database schemas shifted.

The breakthrough came when the lead architect decided to migrate core endpoints to a clean RESTful resource structure, adopting standard HTTP verbs and JSON formatting.

Within two months of the migration, developer onboarding time dropped by 50 percent, and third-party integration support tickets fell by 65 percent, proving the long-term value of RESTful discipline.