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Foff provides official SDKs for TypeScript/JavaScript, Python, and Go. Each SDK follows the same four-step pattern: create a Config, create a client, call getFeatureConfig to resolve the right value for a given hierarchy, and close the client when your process exits. All SDKs poll the Foff API in the background and serve reads from an in-memory cache, so flag lookups are always fast and never block your request path.

TypeScript

Install via npm. Requires Node.js 18+. Works with any Node.js framework.

Python

Install via pip. Requires Python 3.10+. Supports both sync and async clients.

Go

Install via go get. Requires Go 1.22.10+. Thread-safe with goroutine-based polling.

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Minimum runtime requirements

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Common integration pattern

All three SDKs follow the same steps regardless of language.
1

Create a Config

Supply your API key, the base URL, your scope name, and an optional polling interval (in seconds). The polling interval defaults to 30 seconds. Set it to 0 to disable polling.
2

Create a client

Pass your config to the SDK’s client constructor. The client validates your config, makes an initial blocking fetch of all configs for the scope, and starts a background polling loop.
3

Resolve flags with getFeatureConfig

Call getFeatureConfig(featureName, orderedHierarchy) anywhere in your code. Pass the feature name and an ordered list of hierarchy values from least-specific to most-specific (e.g. ["org-1", "team-a", "user-123"]). The SDK resolves the most specific match and falls back to the default value if no override exists.
4

Close the client

Call close() on shutdown to stop background polling and release resources.

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API endpoint

All SDKs call a single endpoint to fetch configs:
The client fetches this endpoint once at startup and then on every polling interval. Reads always come from the in-memory cache — no network call happens when you call getFeatureConfig.

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Hierarchy resolution

When you call getFeatureConfig, the SDK resolves the value from most-specific to least-specific:
  1. It checks the full combination first — e.g. org-1 + team-a + user-123.
  2. It then tries shorter prefixes — org-1 + team-a, then org-1.
  3. If nothing matches, it returns the feature’s default value.
  4. If the feature doesn’t exist at all, it returns null (or nil/None in Go and Python).
This lets you define overrides at any level of your hierarchy and the SDK finds the right one automatically.
Store your API key in an environment variable such as FOFF_API_KEY. Never hard-code it in source files or commit it to version control.