@replayci/replay

ReplayCI's Node.js SDK for deterministic contract validation and passive capture of tool-calling responses.

Installation

Install the SDK with the provider you use:

npm install @replayci/replay openai

npm install @replayci/replay @anthropic-ai/sdk

re2 is optional. If installed, regex invariants run with RE2.

Quick Start

import OpenAI from "openai";
import {
  observe,
  prepareContracts,
  validate,
} from "@replayci/replay";

const client = new OpenAI({ apiKey: process.env.OPENAI_API_KEY });

const observed = observe(client, {
  apiKey: process.env.REPLAYCI_API_KEY,
  agent: "support-bot",
});

const contracts = prepareContracts("./contracts");

const response = await client.chat.completions.create({
  model: "gpt-4o-mini",
  messages: [
    { role: "user", content: "What's the weather in San Francisco?" },
  ],
  tools: [
    {
      type: "function",
      function: {
        name: "get_weather",
        description: "Fetch the weather for a city.",
        parameters: {
          type: "object",
          properties: {
            location: { type: "string" },
          },
          required: ["location"],
        },
      },
    },
  ],
});

const result = validate(response, { contracts });

if (!result.pass) {
  console.error(result.failures);
}

observed.restore();

• validate() checks a single response against your prepared contracts.
• observe() passively captures calls for ReplayCI ingest without changing model behavior.

Docs

Full documentation lives at docs.replayci.com.