How do I combine multiple APIs into one endpoint?

Combining multiple backend APIs into a single endpoint is a practice known as API Aggregation or API Composition. It allows you to shift the burden of orchestrating, fetching, and merging data from mobile apps, web UIs, or AI agents onto the server layer.

Depending on your engineering constraints and technology stack, there are three primary ways to achieve this without building complex, unmaintainable code.

1. The Low-Code/Infrastructure Path: Use an API Gateway If you want to merge multiple REST or microservice endpoints together at the routing layer without writing custom proxy code, an API Gateway is the fastest solution.

How it works: You deploy the gateway as the single public entry point. You then configure a pattern called Gateway Aggregation. When a client hits /api/v1/dashboard, the gateway splits that single incoming call into parallel, independent calls to your backend services internally, waits for them all to finish, bundles the payloads, and returns a single unified JSON object.

Best tools: Kong Gateway (via custom or community aggregation plugins), Apache APISIX, Tyk, or AWS API Gateway.

When to use: When your backend endpoints are stable REST services, and you want to use out-of-the-box infrastructure to save development time.

2. The Frontend-Optimized Path: Backend-for-Frontend (BFF) The BFF pattern involves creating a lightweight, dedicated backend application layer tailored specifically to a single user experience (like a mobile app, a web app, or an AI agent).

How it works: You write a simple API wrapper service (typically using Node.js/TypeScript, Python, or Go). This service exposes exactly the clean endpoints your front end needs. Inside the route handler code, you make multiple asynchronous, parallel HTTP/gRPC requests to your respective target APIs using a library like Axios or Fetch. You then structure and filter the data manually into the perfect layout required by the UI before sending it back.

Best tools: Fastify, Express.js, Next.js API Routes, or FastAPI.

When to use: When you need absolute control over data transformation, custom mapping logic, or filtering out sensitive internal fields before data leaves your infrastructure.

3. The Modern Data Path: A GraphQL Wrapper GraphQL is explicitly designed to solve the problem of endpoint sprawl by letting clients fetch varied resources in a single query round-trip.

How it works: Instead of exposing multiple individual REST endpoints to your client application, you stand up a single GraphQL engine. You define a single Graph schema. In the "Resolver" functions of that GraphQL server, you instruct it to map different fields to different upstream REST or database APIs. The client can then query a massive mix of relational data (e.g., pulling user profiles and order histories simultaneously) using a single POST request to the /graphql endpoint.

Best tools: Apollo Server, GraphQL Mesh (which automatically reads existing Swagger specs and generates a GraphQL wrapper), or Hasura.

When to use: When your frontend requires extreme flexibility, dynamic fields, or when you are building a tool catalog for an AI agent that demands clear schema self-description.

Operational Guardrails for Combined Endpoints When bundling multiple network dependencies behind a single wall, you must plan for failures in the underlying APIs:

Parallelize Requests: Never execute backend API calls sequentially if they do not depend on each other. Use concurrency utilities (like JavaScript’s Promise.all or Python’s asyncio.gather) to minimize execution lag.

Establish Timeouts and Fallbacks: If API #1 completes in 50ms but API #2 drops or stalls, it will break the combined endpoint. Set strict network timeouts. If a non-essential backend service fails, gracefully catch the error and return a partial dataset with a null field rather than failing the entire payload.

Implement Circuit Breakers: If an upstream backend dependency goes down completely, an incoming wave of aggregate endpoint requests can crush it as it attempts to reboot. Utilize a circuit breaker pattern to instantly bypass down services and return cached or default mock values immediately.