Supported Languages

FlagShark supports detection of feature flags across 13 programming languages and all major feature flag providers. This page lists supported languages, file extensions, and SDK patterns.

Language Support Overview

Language	Extensions	Detection Engine	Built-in Providers
TypeScript	.ts, .tsx, .js, .jsx, .mjs, .cjs	AST (tree-sitter)	All 17 — see below
JavaScript	.js, .jsx, .mjs, .cjs	AST (tree-sitter)	All 17 — same as TypeScript
Go	.go	AST (tree-sitter)	All 13 — see below
Python	.py, .pyw, .pyx, .pyi	AST (tree-sitter)	All 13 — see below
Rust	.rs	Regex	LaunchDarkly, Unleash, Flagsmith, ConfigCat, GrowthBook, Eppo
C#	.cs, .csx	Regex	LaunchDarkly, Unleash, Split.io, Optimizely, Flagsmith, ConfigCat, Statsig, GrowthBook, DevCycle, Eppo, PostHog, Microsoft Feature Management
Java	.java	Regex	LaunchDarkly, Unleash, Split.io, Flipt, Optimizely, Flagsmith, ConfigCat, Statsig, GrowthBook, DevCycle, Eppo, PostHog
Kotlin	.kt, .kts	Regex	LaunchDarkly, Unleash, Split.io, Flipt, Optimizely, ConfigCat, Statsig, GrowthBook, DevCycle, Eppo, PostHog
Ruby	.rb, .rake, .gemspec	Regex	LaunchDarkly, Unleash, Split.io, Flipper, Optimizely, Flagsmith, ConfigCat, Statsig, GrowthBook, DevCycle, Eppo, PostHog
PHP	.php, .phtml, .php3, .php4, .php5, .phps	Regex	LaunchDarkly, Unleash, Split.io, Flagsmith, ConfigCat, Statsig, GrowthBook, PostHog, Laravel Pennant
Swift	.swift	Regex	LaunchDarkly, Unleash, Split.io, Optimizely, Flagsmith, ConfigCat, Statsig, GrowthBook, DevCycle, Eppo, PostHog
C++	.cpp, .cc, .cxx, .c++, .hpp, .hh, .hxx, .h++, .h, .c	Regex	LaunchDarkly (Server + Client), Unleash, ConfigCat, GrowthBook
Objective-C	.m, .mm, .h	Regex	LaunchDarkly, Unleash, Split.io, Optimizely, Flagsmith, ConfigCat, PostHog

Detection engines:

• AST (tree-sitter): Structural parse of the syntax tree — survives minification, aliased imports, and unusual whitespace. Enabled by default for TypeScript, JavaScript, Go, and Python; can be overridden per language via engine in .flagshark.yml.
• Regex: Pattern matching on source text. Same provider coverage; slightly more sensitive to unusual formatting.

All languages also detect custom providers configured in .flagshark.yml.

TypeScript & JavaScript

Both languages use the same provider set (JavaScript re-uses the TypeScript detector). The detector reports the language separately based on file extension.

File Extensions

• .ts, .tsx (TypeScript)
• .js, .jsx (JavaScript)
• .mjs, .cjs (ES/CommonJS modules)

Built-in Providers (17)

LaunchDarkly (JS client, Node server, React SDK, legacy Node), Unleash, Split.io, React Feature Flags, Optimizely, Flagsmith, ConfigCat, Flipt, Statsig, GrowthBook, DevCycle, Eppo, PostHog (browser + Node)

LaunchDarkly SDK

// React SDK
import { useFlags, useLDClient } from '@launchdarkly/react-client-sdk';

function MyComponent() {
  // Object destructuring - detected
  const { enableDarkMode, showBetaFeatures } = useFlags();
  
  // Client instance - detected
  const ldClient = useLDClient();
  const value = ldClient?.variation('flag-key', false);
}

// Node.js SDK
import LaunchDarkly from '@launchdarkly/node-server-sdk';

const client = LaunchDarkly.init('sdk-key');
// All variation methods detected
client.variation('flag-key', context, false);
client.boolVariation('flag-key', context, false);
client.stringVariation('flag-key', context, '');
client.intVariation('flag-key', context, 0);
client.jsonVariation('flag-key', context, {});

Unleash SDK

// React SDK
import { useFlag, useVariant } from '@unleash/proxy-client-react';

function MyComponent() {
  const enabled = useFlag('feature-flag');
  const variant = useVariant('feature-flag');
}

// Node.js SDK
import { Unleash } from 'unleash-client';

const unleash = new Unleash({ /* config */ });
unleash.isEnabled('feature-flag');
unleash.getVariant('feature-flag');

Split SDK

// Browser SDK
import { SplitFactory } from '@splitsoftware/splitio';

const factory = SplitFactory({ /* config */ });
const client = factory.client();
client.getTreatment(userKey, 'feature-flag');
client.getTreatments(['flag-1', 'flag-2']);

Go

File Extensions

• .go

Built-in Providers (13)

LaunchDarkly, ZeroFlag, Unleash, Flipt, Split.io, Optimizely, Flagsmith, ConfigCat, Statsig, GrowthBook, DevCycle, Eppo, PostHog

LaunchDarkly SDK

import (
    ld "github.com/launchdarkly/go-server-sdk/v7"
)

func main() {
    client, _ := ld.MakeClient("sdk-key", 5*time.Second)
    
    // All variation methods detected
    enabled, _ := client.BoolVariation("flag-key", context, false)
    str, _ := client.StringVariation("flag-key", context, "default")
    num, _ := client.IntVariation("flag-key", context, 0)
    float, _ := client.Float64Variation("flag-key", context, 0.0)
    json, _ := client.JSONVariation("flag-key", context, ldvalue.Null())
}

Unleash SDK

import "github.com/Unleash/unleash-client-go/v4"

func main() {
    unleash.Initialize(/* config */)
    
    enabled := unleash.IsEnabled("feature-flag")
    variant := unleash.GetVariant("feature-flag")
}

Python

File Extensions

• .py, .pyw, .pyx, .pyi

Built-in Providers (13)

LaunchDarkly, Unleash, Split.io, Flipt, Django Feature Flags, Optimizely, Flagsmith, ConfigCat, Statsig, GrowthBook, DevCycle, Eppo, PostHog

LaunchDarkly SDK

import ldclient
from ldclient import Context

ldclient.set_config(Config("sdk-key"))
client = ldclient.get()

# All variation methods detected
enabled = client.variation("flag-key", context, False)
enabled = client.bool_variation("flag-key", context, False)

Unleash SDK

from UnleashClient import UnleashClient

client = UnleashClient(url="...", app_name="...")
client.initialize_client()

enabled = client.is_enabled("feature-flag")
variant = client.get_variant("feature-flag")

Rust

Detection engine: Regex

File Extensions

• .rs

Built-in Providers (6)

LaunchDarkly, Unleash, Flagsmith, ConfigCat, GrowthBook, Eppo

LaunchDarkly SDK

use launchdarkly_server_sdk::{Client, ConfigBuilder};

fn main() {
    let client = Client::build(ConfigBuilder::new("sdk-key")).unwrap();
    
    // Variation methods detected
    let enabled = client.bool_variation(&context, "flag-key", false);
    let value = client.string_variation(&context, "flag-key", "default");
    let value = client.int_variation(&context, "flag-key", 0);
    let value = client.float_variation(&context, "flag-key", 0.0);
}

C#

Detection engine: Regex

File Extensions

• .cs, .csx

Built-in Providers (12)

LaunchDarkly, Unleash, Split.io, Optimizely, Flagsmith, ConfigCat, Statsig, GrowthBook, DevCycle, Eppo, PostHog, Microsoft Feature Management

LaunchDarkly SDK

using LaunchDarkly.Sdk;
using LaunchDarkly.Sdk.Server;

var client = new LdClient("sdk-key");

// All variation methods detected
bool enabled = client.BoolVariation("flag-key", context, false);
string value = client.StringVariation("flag-key", context, "default");
int value = client.IntVariation("flag-key", context, 0);
double value = client.DoubleVariation("flag-key", context, 0.0);
LdValue value = client.JsonVariation("flag-key", context, LdValue.Null);

Unleash SDK

using Unleash;

var unleash = new DefaultUnleash(config);

bool enabled = unleash.IsEnabled("feature-flag");
Variant variant = unleash.GetVariant("feature-flag");

Java

Detection engine: Regex

File Extensions

• .java

Built-in Providers (12)

LaunchDarkly, Unleash, Split.io, Flipt, Optimizely, Flagsmith, ConfigCat, Statsig, GrowthBook, DevCycle, Eppo, PostHog

LaunchDarkly SDK

import com.launchdarkly.sdk.*;
import com.launchdarkly.sdk.server.*;

LDClient client = new LDClient("sdk-key");

// Variation methods detected
boolean enabled = client.boolVariation("flag-key", context, false);
String value = client.stringVariation("flag-key", context, "default");
int value = client.intVariation("flag-key", context, 0);
double value = client.doubleVariation("flag-key", context, 0.0);
LDValue value = client.jsonValueVariation("flag-key", context, LDValue.ofNull());

Kotlin

Detection engine: Regex

File Extensions

• .kt, .kts

Built-in Providers (11)

LaunchDarkly, Unleash, Split.io, Flipt, Optimizely, ConfigCat, Statsig, GrowthBook, DevCycle, Eppo, PostHog (Android)

LaunchDarkly SDK

import com.launchdarkly.sdk.*
import com.launchdarkly.sdk.server.*

val client = LDClient("sdk-key")

// Variation methods detected
val enabled = client.boolVariation("flag-key", context, false)
val value = client.stringVariation("flag-key", context, "default")
val value = client.intVariation("flag-key", context, 0)

Ruby

Detection engine: Regex

File Extensions

• .rb, .rake, .gemspec

Built-in Providers (12)

LaunchDarkly, Unleash, Split.io, Flipper, Optimizely, Flagsmith, ConfigCat, Statsig, GrowthBook, DevCycle, Eppo, PostHog

LaunchDarkly SDK

require 'ldclient-rb'

client = LaunchDarkly::LDClient.new("sdk-key")

# Variation methods detected
enabled = client.variation("flag-key", context, false)
value = client.variation_detail("flag-key", context, false)

PHP

Detection engine: Regex

File Extensions

• .php, .phtml, .php3, .php4, .php5, .phps

Built-in Providers (9)

LaunchDarkly, Unleash, Split.io, Flagsmith, ConfigCat, Statsig, GrowthBook, PostHog, Laravel Pennant

LaunchDarkly SDK

use LaunchDarkly\LDClient;

$client = new LDClient("sdk-key");

// Variation methods detected
$enabled = $client->variation("flag-key", $context, false);
$enabled = $client->boolVariation("flag-key", $context, false);
$value = $client->stringVariation("flag-key", $context, "default");
$value = $client->intVariation("flag-key", $context, 0);

Swift

Detection engine: Regex

File Extensions

• .swift

Built-in Providers (11)

LaunchDarkly (iOS), Unleash (iOS), Split.io (iOS), Optimizely (iOS), Flagsmith (iOS), ConfigCat (iOS), Statsig (iOS), GrowthBook (iOS), DevCycle (iOS), Eppo (iOS), PostHog (iOS)

LaunchDarkly SDK

import LaunchDarkly

let client = LDClient.get()!

// Variation methods detected
let enabled = client.variation(forKey: "flag-key", defaultValue: false)
let value = client.variation(forKey: "flag-key", defaultValue: "default")

C++

Detection engine: Regex

File Extensions

• .cpp, .cc, .cxx, .c++, .hpp, .hh, .hxx, .h++, .h, .c

Built-in Providers (5)

LaunchDarkly C++ Server SDK, LaunchDarkly C++ Client SDK, Unleash C++ SDK, ConfigCat C++ SDK, GrowthBook C++ SDK

LaunchDarkly C++ Server SDK

#include <launchdarkly/server_side/client.hpp>

// Server SDK: context is the first argument; flag key is at index 1
client->BoolVariation(context, "flag-key", false);
client->StringVariation(context, "flag-key", "default");
client->IntVariation(context, "flag-key", 0);
client->DoubleVariation(context, "flag-key", 0.0);
client->JsonVariation(context, "flag-key", Value::Null());

LaunchDarkly C++ Client SDK

#include <launchdarkly/client_side/client.hpp>

// Client SDK: single-context, flag key is at index 0
client->BoolVariation("flag-key", false);
client->StringVariation("flag-key", "default");
client->IntVariation("flag-key", 0);

Unleash C++ SDK

#include <unleash/unleashclient.h>

client->isEnabled("feature-toggle");
client->getVariant("feature-toggle");

ConfigCat C++ SDK

#include <configcat/configcat.h>

client->getValue("flag-key", false);

GrowthBook C++ SDK

gb->isOn("feature-key");
gb->getFeatureValue("feature-key", fallbackValue);

Objective-C

Detection engine: Regex

File Extensions

• .m, .mm, .h

Built-in Providers (7)

LaunchDarkly (iOS/Objective-C), Unleash (iOS/Objective-C), Split.io (iOS/Objective-C), Optimizely (iOS/Objective-C), Flagsmith (iOS/Objective-C), ConfigCat (iOS/Objective-C), PostHog (iOS/Objective-C)

LaunchDarkly SDK

@import LaunchDarkly;

LDClient *client = [LDClient get];

// Variation methods detected
BOOL enabled = [client boolVariationForKey:@"flag-key" defaultValue:NO];
NSString *value = [client stringVariationForKey:@"flag-key" defaultValue:@"default"];
NSInteger intValue = [client integerVariationForKey:@"flag-key" defaultValue:0];
double doubleValue = [client doubleVariationForKey:@"flag-key" defaultValue:0.0];

Custom Configuration

For custom Objective-C SDKs:

# .flagshark.yml
providers:
  - language: objc
    name: "Custom Obj-C Flags"
    methods:
      - name: "isFeatureEnabled:"
        flagKeyIndex: 0
      - name: "getFeatureValue:default:"
        flagKeyIndex: 0

Adding Custom SDKs

If your SDK isn't listed, you can add custom detection patterns in .flagshark.yml. The schema accepts these keys:

# .flagshark.yml
providers:
  - language: typescript       # required — one of: typescript, javascript, go, python,
                               #   java, kotlin, swift, ruby, csharp, php, rust, cpp, objc
    name: "Internal Feature Flags"
    importPattern: "company/feature-flags"   # optional — only match files that import this
    enabled: true                            # optional — defaults to true
    methods:
      - name: "isEnabled"
        flagKeyIndex: 0        # zero-based index of the flag-key argument
      - name: "getValue"
        flagKeyIndex: 0

The schema is strict — any key not listed above will cause a validation error.

See Configuration for complete details.

Requesting New Language Support

Need support for a language not listed?

Related Documentation

• Flag Detection - How detection works
• Configuration - Custom provider setup
• Flag Not Detected - Troubleshooting