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Feature Flags Rust

PostHogOfficialCreated by PostHog

  • Skill
  • Tool integration
  • Data and AI
  • MIT
  • No issues found

From the author

PostHog feature flags for Rust applications
— the description by PostHog

AutoGineer summary

Written by AutoGineer from the skill’s own files, not by the author

This skill provides guidance and best practices for implementing PostHog feature flags within Rust-based applications. It emphasizes server-side evaluation for performance and consistency, while providing architectural patterns to keep flag logic clean and maintainable. The skill also covers integration with PostHog MCP tools to manage flag lifecycles directly from your development environment.

What it does

  • Provides patterns for integrating PostHog feature flags into Rust codebases.
  • Offers best practices for flag naming, targeting, and lifecycle management.
  • Supports server-side flag evaluation to minimize UI flicker and latency.
  • Facilitates management of feature flags via PostHog MCP tools.
  • Encourages clean code by wrapping flag checks in reusable functions.

When to use it

  • When you need to perform canary releases or feature rollouts in a Rust application.
  • When you want to run A/B tests or experiments on server-side logic.
  • When you need to manage feature flags programmatically using MCP tools.
  • When you want to ensure consistent user experiences across sessions by identifying users correctly.

Advantages

  • Reduces code clutter by promoting centralized flag check functions.
  • Improves performance through server-side local evaluation.
  • Enhances maintainability with clear naming conventions and structured flag usage.
  • Enables direct flag management from the development environment via MCP.

Usage examples

“How do I implement a boolean feature flag in my Rust service?”
The agent will provide a code pattern for checking a flag key and executing conditional logic, while advising on the use of environment variables for configuration.
“Can you help me manage my PostHog feature flags using MCP?”
The agent will check for a connected PostHog MCP server and guide you through using available tools to list, update, or create flags without leaving your IDE.

Install

  1. Download the skill as a ZIP:

    https://autogineer.com/agent-skills/posthog/feature-flags-rust/download
  2. Unzip it into the cross-client skills folder of your project:

    mkdir -p .agents/skills && unzip feature-flags-rust.zip -d .agents/skills

Documentation by PostHog

PostHog feature flags for Rust

This skill helps you add PostHog feature flags to Rust applications.

Reference files

  • references/rust.md - Rust feature flags installation - docs

  • references/adding-feature-flag-code.md - Adding feature flag code - docs

  • references/best-practices.md - Feature flag best practices - docs

Consult the documentation for API details and framework-specific patterns.

Key principles

  • Environment variables: Always use environment variables for PostHog keys. Never hardcode them.

  • Minimal changes: Add feature flag code alongside existing logic. Don't replace or restructure existing code.

  • Boolean flags first: Default to boolean flag checks unless the user specifically asks for multivariate flags.

  • Server-side when possible: Prefer server-side flag evaluation to avoid UI flicker.

PostHog MCP tools

Check if a PostHog MCP server is connected. If available, look for tools related to feature flag management (creating, listing, updating, deleting flags). Use these tools to manage flags directly in PostHog rather than requiring the user to do it manually in the dashboard.

Framework guidelines

No specific framework guidelines.

Files

references/rust.md

Rust feature flags installation - Docs

Install the posthog-rs crate by adding it to your Cargo.toml.

Cargo.toml

PostHog AI

[dependencies]
posthog-rs = "0.3.5"

Next, set up the client with your PostHog project key.

Rust

PostHog AI

let client = posthog_rs::client(env!("<ph_project_token>"));
Blocking client

Our Rust SDK supports both blocking and async clients. The async client is the default and is recommended for most use cases.

If you need to use a synchronous client instead – like we do in our CLI –, you can opt into it by disabling the asynchronous feature on your Cargo.toml file.

toml

PostHog AI

[dependencies]
posthog-rs = { version = "0.3.5", default-features = false }

In blocking mode, calls to capture and related methods will block until the PostHog event capture API returns – generally this is on the order of tens of milliseconds, but you may want to thread::spawn a background thread when you send an event.

Using feature flags

Boolean feature flags

Rust

PostHog AI

let is_enabled = client.is_feature_enabled(
    "flag-key".to_string(),
    "distinct_id_of_your_user".to_string(),
    None, // groups
    None, // person_properties
    None, // group_properties
).await.unwrap();
if is_enabled {
    // Do something differently for this user
}
Multivariate feature flags

Rust

PostHog AI

use posthog_rs::FlagValue;
match client.get_feature_flag(
    "flag-key".to_string(),
    "distinct_id_of_your_user".to_string(),
    None, None, None
).await.unwrap() {
    Some(FlagValue::String(variant)) => {
        if variant == "variant-key" {
            // Do something for this variant
        }
    }
    Some(FlagValue::Boolean(enabled)) => {
        // Handle boolean flag
    }
    None => {
        // Flag not found or disabled
    }
}
Fetching all flags

Rust

PostHog AI

let (flags, payloads) = client.get_feature_flags(
    "distinct_id_of_your_user".to_string(),
    None, None, None
).await.unwrap();
for (key, value) in flags {
    println!("Flag {}: {:?}", key, value);
}
Feature flag payloads

Rust

PostHog AI

let payload = client.get_feature_flag_payload(
    "flag-key".to_string(),
    "distinct_id_of_your_user".to_string()
).await.unwrap();
if let Some(data) = payload {
    println!("Payload: {}", data);
}
With person properties

Rust

PostHog AI

use std::collections::HashMap;
use serde_json::json;
let mut person_props = HashMap::new();
person_props.insert("plan".to_string(), json!("enterprise"));
person_props.insert("country".to_string(), json!("US"));
let flag = client.get_feature_flag(
    "premium-feature".to_string(),
    "distinct_id_of_your_user".to_string(),
    None,
    Some(person_props),
    None
).await.unwrap();
With groups

For B2B applications with group-based flags:

Rust

PostHog AI

use std::collections::HashMap;
use serde_json::json;
let mut groups = HashMap::new();
groups.insert("company".to_string(), "company-123".to_string());
let mut group_props = HashMap::new();
let mut company_props = HashMap::new();
company_props.insert("size".to_string(), json!(500));
group_props.insert("company".to_string(), company_props);
let flag = client.get_feature_flag(
    "b2b-feature".to_string(),
    "distinct_id_of_your_user".to_string(),
    Some(groups),
    None,
    Some(group_props)
).await.unwrap();

Now that you're evaluating flags, continue with the resources below to learn what else Feature Flags enables within the PostHog platform.

ResourceDescription
Creating a feature flagHow to create a feature flag in PostHog
Adding feature flag codeHow to check flags in your code for all platforms
Framework-specific guidesSetup guides for React Native, Next.js, Flutter, and other frameworks
How to do a phased rolloutGradually roll out features to minimize risk
More tutorialsOther real-world examples and use cases
Community questions

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Requirements and compatibility

Works with: Claude Code, Claude apps, OpenAI Codex, GitHub Copilot, Cursor, Gemini CLI, Kiro, OpenCode, Goose, Amp, Roo Code, JetBrains Junie, Factory Droid, Devin (ex-Windsurf), Mistral Vibe, OpenHands, Letta

“Works with” means the tool reads the open Agent Skills format; a skill written for one tool may use features others lack.

Needs: Needs an MCP server

Security

No issues found by our static scan· No issues found

A static scan is not a guarantee. Skills are third-party content: review a skill before you let an agent use it.

Attribution and licence

Created by
PostHog
Publisher
PostHog (Official)
Source
PostHog/skills · skills/posthog/feature-flags/skills/rust · commit a5d30e7
Licence
MIT License (redistribution allowed)
  • LICENSE (added by AutoGineer from LICENSE)
  • ATTRIBUTION.md (written by AutoGineer)
Synced
Also distributed in
PostHog/skills

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Download ZIP

The ZIP holds the skill’s files, its licence files and an ATTRIBUTION.md. Download feature-flags-rust.zip