Every Shipeasy SDK is a thin client over two cached blobs — :flags (gates + configs + kill switches) and :experiments (universes + experiments). The SDK polls them in the background and evaluates locally: there is no per-call network round-trip on your hot path.

The shared evaluation model

All SDKs implement the same contract, so a flag buckets identically whether the call runs in Node, Go, or Swift:

• Deterministic bucketing. The rollout bucket is murmur3("salt:unit") % 10000. The hash is the cross-language MurmurHash3 x86_32 variant (seed 0), verified against shared test vectors — the same user_id lands in the same bucket in every language.
• Local evaluation. Targeting rules, rollout, holdouts, and experiment allocation all run in-process against the polled blob. See Feature gates for the rule model.
• One unit, server + browser. Logged-out traffic buckets on a shared first-party __se_anon_id cookie, so the server and the browser bucket a visitor the same way.
• ETag polling. Each poll sends If-None-Match; a 304 skips the parse. The poll interval is plan-driven and pushed via the X-Poll-Interval header.

Configure once, bind a client

Every SDK leads with the same ergonomic flow: a one-time global configure(...) (server key or client key, plus an optional attributes transform that maps your user object onto the Shipeasy attribute map), then a lightweight, user-bound Client whose getters take no user argument.

import { configure, Client } from "@shipeasy/sdk/server";

configure({
  apiKey: process.env.SHIPEASY_SERVER_KEY!,
  attributes: (u) => ({ user_id: u.id, plan: u.plan }),
});

const flags = new Client(currentUser);
flags.getFlag("new_checkout");

The heavyweight polling state lives in an Engine behind configure() — engine-level features (testing, offline snapshots, onChange, manual exposure, private attributes, sticky bucketing) are configured there. The older per-call getFlag(name, user) form still works on the Engine directly for back-compat.

What every SDK supports

Defaults are returned only when a value can't be evaluated (client not ready, or the key isn't in the blob). A flag that legitimately evaluates false returns false, never the default.

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