Adapters

An adapter (BackendAdapter) is the vendor-neutral evaluate / capture / lifecycle backend behind FireweaveRuntime. You construct one adapter, pass it to the runtime, and share that runtime with FireweaveClient and (optionally) the OpenFeature provider. OpenFeature and the wire still say flagKey. Remote evaluate is POST /v1/flags/evaluate.

Why it exists

Application code should not import a vendor SDK or hold a vendor key on the intended FireWeave path. The runtime owns lifecycle, context bounds, and error mapping. The adapter owns HTTP (or fixtures).

When to use which

Adapter	Use when
FireweaveRemoteAdapter	Production (and any live fw-server). Default network path.
InMemoryAdapter	Unit tests and the offline quickstart. No network.
FireweaveLocalAdapter	Laptop/dev boolean map. Node, Python, Web only.
PostHog adapter	Escape hatch on Python and Go only. Removed from Node 2.1. Java is a seam — `create(config)` returns `UnsupportedCapability`.

How it relates

Concept	Relation
Runtime	Owns initialize / READY / shutdown; default shutdown timeout 10_000 ms
Control points	`adapter.resolve` / evaluate
Targeting	`registerTarget` only on remote (Node/Python/Web)
Exposures / Signals	`POST /v1/capture` on remote
Capabilities	`runtime.backend` and feature flags come from the adapter

Remote — `FireweaveRemoteAdapter`

Production HTTP client to fw-server. Auth: Authorization: Bearer <project key>. Current key prefix in the spec: project-api-key_…. Never send phc_ / phs_ / phx_ on this path.

Path	Purpose	Who implements it
`POST /v1/flags/evaluate`	Batch evaluate, side-effect-free	All five remotes
`POST /v1/capture`	Exposures / signals / events	All five remotes
`POST /v1/targets/register`	Durable target properties	Node, Python, Web remotes only

Binding	Class	Config
Node	`FireweaveRemoteAdapter`	`apiUrl` / `apiKey` or `FW_API_URL` / `FW_PROJECT_API_KEY`. `requestTimeoutMs` 3000, `shutdownTimeoutMs` 10000
Python	`FireweaveRemoteAdapter`	Same env vars when options omitted
Go	`adapters/remote`	`APIURL` / `APIKey` or those env vars. `RequestTimeout` 3s, `CloseTimeout` 10s
Java	`FireweaveRemoteAdapter`	`FireweaveConfig` / constructor only. No `System.getenv`. Javadoc maps `host` / `projectApiKey` to the env names for documentation
Web	`FireweaveRemoteWebAdapter`	`apiUrl` and `apiKey` required. No env. Rejects `phc_` / `phs_` / `phx_` shapes

https is required off-loopback; http is loopback only. Host allowlists differ: Node/Web default to FireWeave hosts + loopback (app-server.fireweave.ai, staging-app-server.fireweave.ai, localhost). Python/Go/Java defaults include PostHog hosts + loopback. Whether app-server.fireweave.ai is the customer-facing URL is NEEDS VERIFICATION.

const adapter = new FireweaveRemoteAdapter({
  apiUrl: process.env.FW_API_URL,
  apiKey: process.env.FW_PROJECT_API_KEY,
  requestTimeoutMs: 3000,
});
const runtime = new FireweaveRuntime(adapter);
const client = new FireweaveClient(runtime);
await client.initialize();

See Configuration for auth and allowlists.

In-memory — `InMemoryAdapter`

Deterministic fixture adapter for tests and offline quickstarts. Present in all five languages (Java: ai.fireweave.testing.InMemoryAdapter; Web: InMemoryWebAdapter). Fixture fields used in tests and SDK docs: type, enabled, value, variant, optional matchAttribute / MatchAttributes, payload, metadata.

const adapter = new InMemoryAdapter({
  flags: {
    'new-checkout': {
      type: 'boolean',
      enabled: true,
      value: true,
      variant: 'on',
    },
  },
});

Node also accepts fault, initError, initGate, and setFlags() for live mutation. Does not implement registerTarget. Registration returns UnsupportedCapability so a harness cannot look registered when it is not. InMemory is not the same class as the local/dev adapter. Node reports InMemory name: 'inmemory' and Local name: 'other'.

Local / dev — Node, Python, Web only

FireweaveLocalAdapter / FireweaveLocalWebAdapter plus makeFireweaveLocalProvider() / make_fireweave_local_provider().

Input: devFlags: Record<string, boolean> (Python equivalent)
Key present → mapped boolean, reason STATIC
Key absent → caller default (FLAG_NOT_FOUND rewritten to DEFAULT on the local provider only)
Boolean-only. Reading an overridden key as string/number → TypeMismatch
No network, no credentials, no exposure sink (exposureEmission: false)

Absent in Go and Java on master. This is not Node in-process secret-key local evaluation. That mode was removed in tree 2.1. Both shipped Node adapters report localEvaluation: false on the remote path; the Local adapter reports localEvaluation: true because it resolves in-process from devFlags.

PostHog extra (language-gated)

Language	Status
Node 2.1	Removed. No `./posthog`, no `PostHogAdapter`, no `posthog-node` peer
Python	`from fireweave.adapters.posthog import PostHogAdapter` — extra `fireweave[posthog]`
Go	package `adapters/posthog`
Java	`PostHogAdapter.create(config)` → `UnsupportedCapability` until a Java server SDK exists
Web	None

Do not document Node PostHogAdapter except on the 2.0 → 2.1 migration page.

Runtime relationship

Construct one runtime per backend. Share it.

Create an adapter
new FireweaveRuntime(adapter) (or language equivalent)
initialize and wait for READY (Web may enter STALE if prefetch loses a 5s ceiling)
Pass the runtime into FireweaveClient and/or FireweaveProvider
shutdown once — flush rules differ on Java

Architecture — layers and wire paths
Configuration — env vars, Java/Web exceptions
Testing — InMemory fixtures
Compatibility — adapter matrix

Get Started

SDKs

Concepts

OpenFeature

Production

Testing

Troubleshooting

Migration

Reference

Why it exists

When to use which

How it relates

Remote — `FireweaveRemoteAdapter`

In-memory — `InMemoryAdapter`

Local / dev — Node, Python, Web only

PostHog extra (language-gated)

Runtime relationship

​Why it exists

​When to use which

​How it relates

​Remote — FireweaveRemoteAdapter

​In-memory — InMemoryAdapter

​Local / dev — Node, Python, Web only

​PostHog extra (language-gated)

​Runtime relationship

​Related

Why it exists

When to use which

How it relates

Remote — `FireweaveRemoteAdapter`

In-memory — `InMemoryAdapter`

Local / dev — Node, Python, Web only

PostHog extra (language-gated)

Runtime relationship

Related