Loglune SDK for Node.js — evaluate feature flags, OpenFeature and CI replay

@loglune/sdk is the evaluation client for Loglune: send an evaluation context, get back every feature flag's result (or one flag's) and the evaluation record a bug report carries. The Loglune server evaluates; the package sends the request and returns the server's answer.

Install

The SDK requires Node.js 22 or later, or any runtime with a global fetch.

npm install @loglune/sdk

Evaluate flags for a user

Mint an SDK key under SDK keys at /app/author, then create a client with it.

import { createLogluneClient } from '@loglune/sdk';

const loglune = createLogluneClient({ sdkKey: process.env.LOGLUNE_SDK_KEY });
const { result, record } = await loglune.evaluateOne('new-checkout', {
  key: userId,
  attributes: { plan: 'pro' }
});

Option	Required	Meaning
`sdkKey`	yes	the SDK key
`version`	no	a published version to evaluate (replay); absent evaluates the current version
`baseUrl`	no	the Loglune origin (default `https://loglune.com`)
`fetch`	no	a fetch implementation (default the global `fetch`)

Call	Returns
`evaluateAll(context)`	`{ results, record }`, one result per flag
`evaluateOne(flagKey, context)`	`{ result, record }`; `result.reason.kind` is `flagNotFound` when the version lacks the flag

Attach record to a bug report. The record holds the version, an opaque context key (never the raw key), the results, the instant and the attribute names (never their values).

Errors

A refusal throws LogluneError with the fields of the server's answer: status, error, reason, hint (what to do next), retryAfter and issues (the fields to fix). A network failure throws the fetch error.

Use Loglune as an OpenFeature provider

import { OpenFeature } from '@openfeature/server-sdk';
import { createLogluneClient } from '@loglune/sdk';
import { createLogluneProvider } from '@loglune/sdk/openfeature';

await OpenFeature.setProviderAndWait(
  createLogluneProvider({ client: createLogluneClient({ sdkKey: process.env.LOGLUNE_SDK_KEY }) })
);

@openfeature/server-sdk is an optional peer dependency of @loglune/sdk; install it only to use the @loglune/sdk/openfeature entry.

Replay a past flag state in CI

import { runReplayRegression } from '@loglune/sdk/ci-replay';

const report = await runReplayRegression(
  { sdkKey: process.env.LOGLUNE_SDK_KEY, version: 42, at: '2026-08-22T14:07:00Z' },
  [{ context: { key: 'user-1', attributes: { plan: 'pro' } }, expect: { 'new-checkout': 'on' } }]
);
if (!report.ok) process.exit(1);

runReplayRegression evaluates each case against the pinned version at at, unless the case sets evaluatedAt. report.ok is false when any flag resolved to another variation or is missing, and the example then exits with code 1 to fail the CI step.