Skip to main content

Fastify Backend Server

This example demonstrates a minimal Fastify backend exposing standard OpenAI-compatible HTTP endpoints using the @caesura-io/openai wrapper.

Source Code: caesura-io/examples-sdk-js/examples/node-openai-server

What this shows​

A server-side integration wrapping the official OpenAI Node SDK, logging injected recommendations and credit usage to the console. It uses gpt-5.4-mini via both the newer Responses API and the older Chat Completions API.

When to use it: Use the @caesura-io/openai package when you are building a headless service, backend worker, or an application that already uses the official openai package directly.

Prerequisites​

  • Node.js v22 or higher
  • An OpenAI API key
  • A Caesura API key (see Authentication)

Setup​

  1. Clone the examples repository.
  2. Navigate to the example directory: 
    cd examples/node-openai-server
  3. Copy the example environment file: 
    cp .env.example .env
  4. Fill in your OPENAI_API_KEY and CAESURA_API_KEY in .env. Ensure your Caesura environment base URL is correctly set if you are not using the default.
  5. Install dependencies: 
    npm install

Run​

Run the server using Node's native --env-file support and tsx (which executes TypeScript directly):

npm run dev

Note: The dev script in package.json maps to npx tsx --env-file=.env src/server.ts.

What you'll see​

You can use the included requests.http file (or curl) to ping the server.

In your console, you will see Fastify startup logs alongside detailed Caesura lifecycle events:

  • The requests sent to Caesura's backend for analysis
  • The resulting recommendations
  • When a recommendation is injected into your OpenAI request

Data Flow​

Because Caesura operates as a middleware/proxy, it is important to understand where your data goes:

  • Provider API Key (OpenAI): Sent only to OpenAI. It is never sent to the Caesura backend. This key remains securely on your server.
  • Conversation Content: Sent to the Caesura backend for analysis, and to the provider for language model generation.
  • Caesura API Key: Sent only to the Caesura backend.