Which SDK do I need?

Every Checkgate SDK wraps the same shared Rust evaluation core, so a flag resolves identically on a server, in a browser, and on a phone. What differs is only how the core is embedded (NAPI, WebAssembly, JSI, FFI) and where the flag snapshot comes from.

Find your stack below — each section lists what's required, what's optional, and why.

At a glance

Your stack	Required	Optional
Next.js / Remix / SvelteKit / Nuxt (server-rendered)	@checkgate/web + @checkgate/ssr	@checkgate/edge, @checkgate/cli
Next.js — server-only flags (no client usage)	@checkgate/node	@checkgate/cli
SPA — Vite, Vue, React, Svelte, Angular	@checkgate/web	@checkgate/cli
React Native	@checkgate/react-native	@checkgate/cli
Flutter	checkgate_flutter	@checkgate/cli
Node.js server — Express, Fastify, NestJS	@checkgate/node	@checkgate/cli
Edge — Cloudflare Workers, Vercel Edge, middleware	@checkgate/edge + @checkgate/web	@checkgate/cli

@checkgate/cli is optional everywhere — it's a dev-time tool that generates type-safe flag accessors. It never ships in your runtime bundle.

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Web frameworks with a server (Next.js, Remix, SvelteKit, Nuxt)

There are two valid setups. Pick based on where you read flags.

A. Flags used in the browser → zero-flicker SSR

npm install @checkgate/web @checkgate/ssr

This is the setup most apps want. Without it, a client-side SDK shows default values until its stream connects, so the "old" UI paints first and snaps to the "new" one a moment later.

• @checkgate/web (required) — the live client SDK. It also exports the shared WASM engine at @checkgate/web/core, which resolves flags on the server. On Node it loads the engine from disk, so await createWasmCore() takes no arguments.
• @checkgate/ssr (required) — the glue. buildBootstrap() resolves flags server-side, bootstrapScriptTag() embeds them in the document, and readBootstrap() + BootstrapValues give the first client render the exact values the server used — so React hydration matches and nothing flickers. It has zero dependencies and ships no engine of its own.
• @checkgate/edge (optional) — adds TTL-cached snapshot fetching so you aren't re-fetching /flags/snapshot on every request. Skip it and fetch the snapshot yourself, passing it straight to buildBootstrap({ snapshot }).

See the SSR / Bootstrap guide for the full three-step flow.

B. Flags only read on the server

npm install @checkgate/node

If flags never reach the browser — server components, route handlers, API routes — the Node SDK alone is enough. It keeps a live SSE connection and isEnabled() is a synchronous in-memory call, so there's no per-request network round-trip and nothing to hydrate.

TIP

@checkgate/node is a native addon and runs in the Node.js runtime only. For Next.js middleware or any route set to the edge runtime, use @checkgate/edge + @checkgate/web/core instead.

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SPA — Vite, Vue, React, Svelte, Angular

npm install @checkgate/web

One package, nothing else. A pure SPA has no server render, so there's no bootstrap to embed and nothing to hydrate — @checkgate/ssr would do nothing for you.

@checkgate/web compiles the evaluation core to WebAssembly and runs it in the browser: it streams flag updates over SSE, evaluates locally at near-native speed, and falls back to polling /flags/snapshot if the stream can't reconnect.

import { CheckgateWeb } from '@checkgate/web'

const client = new CheckgateWeb({
  serverUrl: import.meta.env.VITE_CHECKGATE_URL,
  sdkKey: import.meta.env.VITE_CHECKGATE_SDK_KEY,
})
await client.connect()

client.isEnabled('new-homepage', userId)

See the Web SDK reference for the React and Vue examples.

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Mobile

React Native

npm install @checkgate/react-native

One package. The Rust core is embedded through JSI, so evaluation is a direct synchronous call into native code with no bridge hop and no JSON serialization per call. Native compilation happens inside your app's Xcode / Gradle build via the included podspec and CMakeLists — there's no separate binary to fetch.

See the React Native SDK reference.

Flutter

flutter pub add checkgate_flutter

One package. The same core is bound through Dart FFI. Note this is a pub.dev package — the @checkgate/* npm packages are not involved.

See the Flutter SDK reference.

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Node.js server (Express, Fastify, NestJS)

npm install @checkgate/node

One package. The core is embedded via NAPI, so isEnabled() is a synchronous in-memory lookup — safe to call in a hot request path. The client holds one SSE connection per process and updates its local store as flags change, so a flag flip reaches every server in milliseconds without polling.

const { CheckgateClient } = require('@checkgate/node')

const client = new CheckgateClient({
  serverUrl: process.env.CHECKGATE_URL,
  sdkKey: process.env.CHECKGATE_SDK_KEY,
})
await client.connect()

app.get('/', (req, res) => {
  if (client.isEnabled('new-homepage', req.user.id)) { /* … */ }
})

See the Node.js SDK reference.

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Edge runtimes (Cloudflare Workers, Vercel Edge, middleware)

npm install @checkgate/edge @checkgate/web

Edge isolates are short-lived and can't hold a long-running SSE connection, so the edge client fetches a snapshot instead and caches it in memory with a TTL plus stale-while-revalidate.

• @checkgate/edge (required) — snapshot fetching, caching, and refresh.
• @checkgate/web (required) — supplies the evaluation engine via @checkgate/web/core. In Workers, pass the wasm module explicitly, since Wrangler compiles a .wasm import into a WebAssembly.Module:

import { createWasmCore } from '@checkgate/web/core'
import wasmModule from '@checkgate/web/dist/checkgate_bg.wasm'

const core = await createWasmCore(wasmModule)

See the Edge evaluation guide.

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Optional everywhere: type-safe flag accessors

npm install -D @checkgate/cli

@checkgate/cli generates typed accessors from your live flags for TypeScript, Rust, and Dart — so a renamed or deleted flag becomes a compile error instead of a silent false. It's a dev dependency and never ships in your runtime bundle. See the CLI guide.

Not evaluation SDKs

These manage flags rather than evaluate them, and are unrelated to your app's runtime:

• Terraform / OpenTofu provider — manage flags and segments as code.
• Kubernetes operator — reconcile FeatureFlag custom resources into Checkgate.
• checkgate-go — the shared Go REST client backing both of the above; also usable directly for automation that creates or updates flags.