--- description: Set up the FlagshipClientProvider to evaluate feature flags synchronously in browser applications using the OpenFeature web SDK. title: TypeScript Client SDK image: https://developers.cloudflare.com/og-docs.png --- [Skip to content](#main-content) > Documentation Index > Fetch the complete documentation index at: https://developers.cloudflare.com/flagship/llms.txt > Use this file to discover all available pages before exploring further. # TypeScript Client SDK Last updated Aug 24, 2026|Copy as Markdown|[View as Markdown](https://docs-durable-objects-instance-replaced-errors.previews.developers.cloudflare.com/flagship/sdk/client-provider/index.md)|[Agent setup](https://docs-durable-objects-instance-replaced-errors.previews.developers.cloudflare.com/agent-setup/) The `FlagshipClientProvider` implements the OpenFeature web provider interface for browser applications. It pre-fetches a declared set of flag values on initialization and resolves evaluations synchronously from an in-memory cache. This makes the provider suitable for client-side rendering where synchronous access to flag values is required. Caution We do not recommend using the client provider in public-facing apps right now. It requires a Cloudflare API token, which would be exposed in client-side code and visible to anyone who inspects your application. We are working on a safer solution for client-side flag evaluation — in the meantime, use the [Worker binding](https://docs-durable-objects-instance-replaced-errors.previews.developers.cloudflare.com/flagship/binding/) or the [TypeScript server SDK](https://docs-durable-objects-instance-replaced-errors.previews.developers.cloudflare.com/flagship/sdk/server-provider/). ## prefetchFlags `prefetchFlags` is a required array of flag keys that the provider fetches during initialization and on every context change. Only flags listed in this array are available for synchronous evaluation — any flag key not included returns a `FLAG_NOT_FOUND` error at resolution time. **Fetch behavior:** * **On initialization** — all flags in `prefetchFlags` are fetched in parallel and stored in an in-memory cache. The provider transitions to `READY` once all fetches complete (individual failures are non-fatal). * **On context change** — the cache is invalidated and all flags are re-fetched for the new context. This is required by the [static context paradigm ↗](https://openfeature.dev/specification/glossary/#static-context-paradigm) used by the OpenFeature web SDK, where context is set globally and providers are expected to re-evaluate when it changes. * **At resolution time** — evaluations are served synchronously from the cache. No network request is made during `getBooleanValue`, `getStringValue`, etc. ## Setup The following example initializes the provider with a set of pre-fetched flags and evaluates them in a browser application. ```js import { OpenFeature } from "@openfeature/web-sdk"; import { FlagshipClientProvider } from "@cloudflare/flagship/web"; await OpenFeature.setProviderAndWait( new FlagshipClientProvider({ appId: "", accountId: "", authToken: "", prefetchFlags: ["promo-banner", "dark-mode", "max-uploads"], }), ); // Set evaluation context globally. The provider re-fetches all prefetchFlags // whenever the context changes. await OpenFeature.setContext({ targetingKey: "user-42", plan: "enterprise" }); const client = OpenFeature.getClient(); // Synchronous — served from the in-memory cache. const showBanner = client.getBooleanValue("promo-banner", false); if (showBanner) { document.getElementById("banner").style.display = "block"; } ``` ```ts import { OpenFeature } from "@openfeature/web-sdk"; import { FlagshipClientProvider } from "@cloudflare/flagship/web"; await OpenFeature.setProviderAndWait( new FlagshipClientProvider({ appId: "", accountId: "", authToken: "", prefetchFlags: ["promo-banner", "dark-mode", "max-uploads"], }), ); // Set evaluation context globally. The provider re-fetches all prefetchFlags // whenever the context changes. await OpenFeature.setContext({ targetingKey: "user-42", plan: "enterprise" }); const client = OpenFeature.getClient(); // Synchronous — served from the in-memory cache. const showBanner = client.getBooleanValue("promo-banner", false); if (showBanner) { document.getElementById("banner").style.display = "block"; } ``` Note `getBooleanValue` on the client provider is synchronous and does not require `await`, unlike the [TypeScript server SDK](https://docs-durable-objects-instance-replaced-errors.previews.developers.cloudflare.com/flagship/sdk/server-provider/). ## Configuration options | Option | Type | Required | Description | | ------------- | ----------- | -------- | --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | appId | string | Yes | The Flagship app ID from the Cloudflare dashboard. | | accountId | string | Yes | Your Cloudflare account ID. | | authToken | string | Yes | A Cloudflare [API token](https://docs-durable-objects-instance-replaced-errors.previews.developers.cloudflare.com/fundamentals/api/get-started/create-token/) with Flagship read permissions. | | fetchOptions | RequestInit | No | Custom fetch options applied to HTTP requests. | | timeout | number | No | Request timeout in milliseconds. Defaults to 5000. | | retries | number | No | Retry attempts on transient errors. Defaults to 1 and is capped at 10. | | retryDelay | number | No | Delay between retries in milliseconds. Defaults to 1000 and is capped at 30000. | | prefetchFlags | string\[\] | Yes | Flag keys to fetch on initialization and on every context change. Flags not in this list return FLAG\_NOT\_FOUND at evaluation time. | ## When to use the client provider Use the client provider in browser applications, single-page apps, or any client-side JavaScript environment. Evaluations are synchronous, so they do not block rendering. Flag values are fetched once during initialization and re-fetched whenever the evaluation context changes. To force a refresh, update the context via `OpenFeature.setContext(...)`. Was this helpful? YesNo ## On this page [![](https://docs-durable-objects-instance-replaced-errors.previews.developers.cloudflare.com/_astro/logo.te5VL_aD.svg)Docs](https://docs-durable-objects-instance-replaced-errors.previews.developers.cloudflare.com/) ```json {"@context":"https://schema.org","@type":"TechArticle","@id":"https://developers.cloudflare.com/flagship/sdk/client-provider/#page","headline":"TypeScript Client SDK · Cloudflare Flagship docs","description":"Set up the FlagshipClientProvider to evaluate feature flags synchronously in browser applications using the OpenFeature web SDK.","url":"https://developers.cloudflare.com/flagship/sdk/client-provider/","inLanguage":"en","image":"https://developers.cloudflare.com/og-docs.png","dateModified":"2026-08-24","publisher":{"@type":"Organization","name":"Cloudflare","description":"One platform for your apps, agents, and workforce. 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