---
description: Set up the Flagship OpenFeature provider to evaluate Flagship feature flags from Go server applications.
title: Go SDK
image: https://developers.cloudflare.com/og-docs.png
---

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# Go SDK

Last updated Aug 24, 2026|Copy as Markdown|[View as Markdown](https://e8aee267.previews.developers.cloudflare.com/flagship/sdk/go/index.md)|[Agent setup](https://e8aee267.previews.developers.cloudflare.com/agent-setup/)

The Go SDK provides an OpenFeature-compatible server provider for Go applications. It evaluates flags over HTTP and does not support the Cloudflare Workers binding.

## Installation

Install with `go get`:

```sh
go get github.com/cloudflare/flagship/sdks/go
```

## Setup

Configure the provider with your Flagship app ID, Cloudflare account ID, and an API token with Flagship Evaluate permission.

```go
package main

import (
	"context"
	"log"

	flagship "github.com/cloudflare/flagship/sdks/go"
	"github.com/open-feature/go-sdk/openfeature"
)

func main() {
	ctx := context.Background()

	provider, err := flagship.NewProvider(flagship.Options{
		AppID:     "<APP_ID>",
		AccountID: "<ACCOUNT_ID>",
		AuthToken: "<API_TOKEN>",
	})
	if err != nil {
		log.Fatal(err)
	}

	if err := openfeature.SetProviderAndWait(provider); err != nil {
		log.Fatal(err)
	}
	defer openfeature.Shutdown()

	client := openfeature.NewDefaultClient()
	evalCtx := openfeature.NewEvaluationContext("user-42", map[string]any{
		"plan": "enterprise",
	})

	enabled, err := client.BooleanValue(ctx, "new-checkout", false, evalCtx)
	if err != nil {
		log.Fatal(err)
	}

	log.Println("new-checkout:", enabled)
}
```

## Flag types

The Go SDK supports all OpenFeature server-side flag types.

```go
enabled, _ := client.BooleanValue(ctx, "new-checkout", false, evalCtx)
variant, _ := client.StringValue(ctx, "homepage-hero", "control", evalCtx)
rate, _ := client.FloatValue(ctx, "sample-rate", 0.1, evalCtx)
limit, _ := client.IntValue(ctx, "upload-limit", 10, evalCtx)
config, _ := client.ObjectValue(ctx, "ui-config", map[string]any{"theme": "light"}, evalCtx)
```

Use the `*ValueDetails` methods when you need reason, variant, metadata, or error codes.

## Response caching

The provider can cache evaluations to avoid a network round-trip for repeated flag/context pairs. Caching is off by default and enabled by setting `CacheTTL`:

```go
provider, err := flagship.NewProvider(flagship.Options{
	AppID:        "<APP_ID>",
	AccountID:    "<ACCOUNT_ID>",
	AuthToken:    "<API_TOKEN>",
	CacheTTL:     30 * time.Second, // values may be up to this stale
	CacheMaxSize: 1000,             // LRU-evicted beyond this many entries
})
```

Each cache entry is keyed by flag key, flag type, and the full evaluation context, so distinct contexts never share a cached value. Cache hits resolve with `reason == openfeature.CachedReason`.

Disabled flags, errors, and type mismatches are never cached. Because freshness is TTL-based, a flag change in Flagship takes effect after the entry expires.

The cache is per-provider instance, guarded by a mutex for concurrent use, and cleared on `Shutdown`.

## Configuration options

| Option         | Description                                                                                              |
| -------------- | -------------------------------------------------------------------------------------------------------- |
| AppID          | Flagship app ID.                                                                                         |
| AccountID      | Required with AppID.                                                                                     |
| BaseURL        | Base URL override. Defaults to https://api.cloudflare.com.                                               |
| AuthToken      | Adds Authorization: Bearer <token> to each request.                                                      |
| Headers        | Static headers. Explicit Authorization overrides AuthToken.                                              |
| HeadersFactory | Dynamic per-request headers. Values override Headers and AuthToken.                                      |
| HTTPClient     | Custom HTTP client.                                                                                      |
| Timeout        | Per-attempt timeout. Defaults to 5 seconds.                                                              |
| Retries        | Retry attempts on transient errors. Defaults to 1 and is capped at 10.                                   |
| DisableRetries | Disables retries when set to true.                                                                       |
| RetryDelay     | Delay between retries. Defaults to 1 second and is capped at 30 seconds.                                 |
| CacheTTL       | Enables in-memory response caching when greater than 0\. Cached values may be up to this duration stale. |
| CacheMaxSize   | Maximum number of cached entries. LRU-evicted beyond this limit. Defaults to 1000 when CacheTTL is set.  |
| Logging        | Enables debug and error logging. Off by default.                                                         |
| Logger         | Optional slog\-compatible logger. Uses the default slog logger when unset.                               |
| Hooks          | Provider-level OpenFeature hooks.                                                                        |

## Evaluation context

Context attributes are sent as URL query parameters. Supported values are strings, numeric types, booleans, and `time.Time`. `nil` values are skipped. Maps, slices, structs, and other complex values return `INVALID_CONTEXT` through OpenFeature and do not trigger an HTTP request.

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