What is a feature toggle?

A feature toggle (also called a feature flag or feature switch) is a conditional statement in your codebase that lets you turn functionality on or off at runtime without deploying new code. Instead of removing or commenting out code during development, you wrap it in a toggle that responds to configuration changes stored outside your application.

The technical implementation is straightforward. You add an if statement that checks whether a feature is enabled for the current user before executing the corresponding code path. The state of that toggle lives in a feature flag system separate from your application, which means you can change behavior without redeploying.

How feature toggles work

At the code level, a feature toggle is a conditional check. Your application queries a feature flag system to determine whether a specific flag is enabled for the current user, then executes the appropriate code branch based on that state.

The flag’s configuration exists in a separate system. This decoupling means you can modify which users see which features, adjust rollout percentages, or disable problematic code without touching your application’s source or going through a full deployment cycle.

When your application starts or at defined intervals, it retrieves the current state of all relevant flags. Most implementations cache these states locally to minimize latency. The application then evaluates each flag based on the context you provide (user ID, location, device type, or custom attributes).

Types of feature toggles

Different use cases require different toggle patterns. The type determines how long the toggle should exist and how you manage it.

Release toggles support trunk-based development by hiding incomplete features in production. When you merge code to the main branch before it’s ready for users, a release toggle keeps it inactive until you’re prepared to expose it. These toggles typically last 40 days or less, roughly the time between starting a feature and completing its rollout.

Experiment toggles facilitate A/B testing and multivariate experiments. Unleash lets you expose different variants of a feature to different user segments, then measure which performs better. Like release toggles, experiments usually run for around 40 days, just long enough to gather statistically significant data.

Operational toggles control system behavior at runtime. You might use them to enable a new algorithm, switch between service implementations, or adjust resource usage based on load. These toggles tend to have shorter lifespans (around 7 days) because Unleash considers them to address specific operational needs rather than long-term feature development.

Permission toggles (or entitlement toggles) control access to premium features or functionality based on user tier. Unlike other toggle types, permission toggles often remain in your codebase permanently as part of ongoing business logic rather than transitional development states.

Kill switches provide emergency shutoff capability for critical situations. When a severe bug appears or a performance problem threatens system stability, you can disable the affected feature immediately without rolling back your entire deployment. These toggles exist as long as the corresponding features do.

Feature toggles versus feature branches

Feature branches and feature toggles both address the problem of integrating incomplete work, but Unleash operates at different layers and produces different outcomes than traditional branching strategies.

A feature branch isolates new code in a separate Git branch. You develop there until the feature is complete, then merge it back to the main branch. This keeps broken code out of the main codebase, but it creates integration problems. The longer a branch lives, the more it diverges from main, and the harder the eventual merge becomes. Testing also becomes complicated because you need to set up separate environments for each branch.

Feature toggles eliminate long-lived branches by allowing incomplete code in the main branch. The toggle hides unfinished functionality from users while letting developers commit frequently. You deploy to production continuously, but the toggle controls when users see the new code.

This approach provides faster feedback. Your code runs in the actual production environment from day one, so you catch environment-specific issues early. Multiple teams can work on overlapping parts of the codebase without complex branch management. When you’re ready to release, you modify the toggle’s configuration rather than coordinating a merge and deployment.

The tradeoff is code complexity. Your codebase contains multiple conditional paths, and you need to maintain the toggle infrastructure. Feature branches keep experimental code completely separate but at the cost of integration difficulties. Feature toggles integrate continuously but add conditional logic to your production code.

Activation strategies

A toggle can be either on or off globally, but that binary control doesn’t cover most real situations. Activation strategies define the rules that determine which users see which features.

The gradual rollout strategy exposes a feature to a percentage of your traffic. You might start at 5%, monitor for issues, then increase to 25%, 50%, and eventually 100%. The rollout uses consistent hashing on user IDs so each user sees the same experience across sessions.

User targeting activates features for specific users or segments. You can target by user ID, email domain, geographic region, device type, or any custom attribute your application provides. This is useful when beta testing with specific customers or rolling out features regionally.

Constraint-based strategies add conditions to other strategies. You might combine a gradual rollout with a time constraint so the feature only activates during business hours, or limit a rollout to users in specific countries.

Segments group multiple constraints into reusable configurations. Instead of adding the same set of constraints to every toggle, you define a segment once (like “power users in Europe”) and reference it across multiple flags.

Strategy variants

Beyond controlling who sees a feature, variants let you control what version each user sees. This supports A/B testing and experimentation.

When you configure variants on a toggle, you assign each variant a name, a weight (the percentage of users who should receive it), and optionally a payload containing additional data. Unleash consistently assigns the same variant to each user based on a stickiness parameter.

For example, you might create three variants of a checkout flow: control (30%), variant A (35%), and variant B (35%). Each user consistently sees the same variant, and you can compare conversion rates across the three groups. The payload can include different feature configurations, UI parameters, or backend settings specific to that variant.

Projects and environments

Feature toggles exist within organizational structures that map to your development workflow.

Environments represent deployment stages like development, staging, and production. A single toggle has independent configurations in each environment. You might enable a toggle for all users in development, 10% in staging, and keep it off in production. When you’re satisfied with testing, you modify the production configuration without changing code or redeploying.

Projects organize toggles by ownership or domain. You might create projects per team, per microservice, or per product area. Projects provide access control boundaries and help manage flags at scale. A team with access to the payments project can modify its toggles without affecting other teams’ flags.

The combination gives you flexibility. A cross-functional team can own a project containing all toggles for their product area. Within that project, Unleash lets them independently manage rollouts across development, staging, and production environments.

Managing toggle lifecycle

Feature toggles require active management to prevent technical debt. Toggles that outlive their purpose clutter your codebase and create maintenance burden.

Lifecycle stages track a toggle’s progression from creation through cleanup:

• Define: The toggle exists but hasn’t received any usage metrics
• Develop: The toggle is active in pre-production environments
• Production: Users in production are seeing the feature
• Completed: You’ve finished the rollout and marked the toggle for cleanup
• Archived: The toggle is no longer in use

Moving through these stages requires deliberate action. When you finish rolling out a feature, you mark the toggle as completed. This signals to your team that the toggle should be removed from the codebase. Unleash generates events when toggles become stale, which you can use to trigger notifications, break builds, or open pull requests for cleanup.

Toggle types influence expected lifetime. Release and experiment toggles should be short-lived (weeks to months). Operational toggles might last longer depending on your needs. Permission toggles and kill switches can be permanent. If a toggle exceeds its expected lifetime, that indicates a problem in your development process.

Common patterns

Several patterns emerge when using feature toggles at scale:

When rolling out a major feature, create a single toggle that controls the entire feature across all services. This gives you one switch to control the rollout and ensures all components enable simultaneously.

For operational flags that might stay long-term, document their purpose and assign clear ownership. These flags become part of your application’s operational controls and need the same care as other production systems.

Test both code paths while a toggle is active. Run tests with the feature on and off to catch issues in either branch. When you remove the toggle, delete the old code path completely rather than leaving it commented out.

Use consistent naming conventions. Include the toggle type, team or domain, and feature name in the flag identifier. This makes it easier to identify orphaned toggles and understand their purpose without checking documentation.

Implement monitoring for toggle state changes and performance impact. Track when toggles get modified, who changed them, and how features behave when enabled. This observability helps debug issues and audit your release process.

Set up automated cleanup. Configure your CI pipeline to fail builds that contain stale toggles, or use webhooks to open pull requests removing toggles marked for deletion. Automation prevents flags from accumulating in your codebase indefinitely.

Frequently asked questions

How is a feature toggle different from a configuration setting?

Configuration settings change system parameters like database connection strings or API endpoints. Feature toggles control whether entire code paths execute. While both externalize decisions from code, toggles specifically manage feature availability and are designed to be temporary.

Do feature toggles slow down my application?

The performance impact is minimal. Most SDKs cache flag states in memory and evaluate them locally. A typical flag evaluation takes microseconds. Network requests to fetch flag states happen in the background and don’t block your application logic.

When should I remove a feature toggle?

Remove release toggles once you’ve rolled out the feature to 100% of users and confirmed it’s working. Remove experiment toggles after you’ve collected enough data and selected a winning variant. Operational toggles and kill switches can stay longer if they serve an ongoing purpose.

Can I use feature toggles for configuration management?

Feature toggles can carry payloads with configuration data through variants, but this isn’t their primary purpose. Use toggles to control whether features run and variants to test different configurations. For general application config, standard configuration management tools are more appropriate.

How many feature toggles should I have?

The number depends on your release cadence and team size. Organizations with frequent deployments and multiple teams naturally accumulate more toggles. What matters more than the total count is active lifecycle management. Regularly archive completed toggles to prevent accumulation.