Feature Flags Architecture for SaaS Checklist

Use this checklist before implementing feature flags in a new SaaS product and before scaling an existing flag system. Each item represents a decision that is expensive to undo after flags are in production.

✅ Before You Implement

• → Chosen a flag storage strategy — database-backed (flexible, queryable), config file (simple, requires deploy), or hosted service (LaunchDarkly, Unleash, Flagsmith). Database-backed is the recommended default for early-stage SaaS.
• → Defined flag naming convention — use a consistent prefix pattern: feature_[area]_[name] (e.g., feature_billing_annual_toggle). Inconsistent names become unmaintainable at 50+ flags.
• → Established flag type taxonomy — at minimum: release flags (temporary), experiment flags (A/B tests), ops flags (kill switches), and permission flags (plan-based). Each has different lifecycle rules.
• → Decided on evaluation location — server-side evaluation (more secure, less latency-sensitive) vs. client-side evaluation (faster UI response, requires SDK). Default to server-side; add client-side only when UI performance requires it.
• → Set a default state policy — what happens when a flag lookup fails or the flag does not exist? Default to OFF (feature disabled) for safety. Never default to ON for unreleased features.

✅ Flag Design

• → Each flag controls exactly one behavior — flags that gate multiple behaviors create cross-cutting dependencies that are hard to clean up.
• → Targeting rules are documented at flag creation — who sees this flag enabled, and why. Undocumented targeting rules become permanent mysteries.
• → Boolean by default — use multivariate flags (string/JSON values) only when the use case genuinely requires more than on/off. Complexity compounds.
• → Expiry date set for all release flags — release flags should be temporary. Assign a cleanup date at creation; flag debt is real technical debt.
• → Kill switch flags are separated from release flags — kill switches need to be findable and operable under pressure. Keep them in a dedicated namespace and document them separately.

✅ Targeting and Rollout

• → Rollout is percentage-based, not all-or-nothing — release to 5%, then 20%, then 100%. Gradual rollout catches issues before they affect all users.
• → Targeting is by account/tenant, not individual user — for B2B SaaS, flag targeting at the account level prevents the same account seeing mixed experiences across users.
• → Internal team is a targeting segment — your own team should see all flags before external users. Create an "internal" segment and use it for every new flag.
• → Stickiness is configured — users should not flip between flag states on refresh. Ensure your flag system uses a consistent hashing strategy tied to user or account ID.

✅ Cleanup and Maintenance

• → A flag cleanup process exists — weekly or monthly review of flags past their expiry date. Stale flags are removed from code before the flag is deleted from the system.
• → Removal is two-step — first remove the flag check from code (deploy), then delete the flag from the flag store. Never delete the flag record before removing the code reference.
• → Flag count is monitored — alert when active flag count exceeds a threshold (e.g., 50 active flags). High flag counts signal cleanup debt.
• → Flag state changes are logged — who changed a flag, when, and to what state. This is an audit trail requirement for any compliance-adjacent product.

What to Do Next

Run through this checklist before your first flag goes live. If you already have flags in production: audit your existing flags against the cleanup and naming items — those are where accumulated debt shows up first. If your flag count is over 30 and you have no cleanup process: schedule a flag audit sprint before adding new flags.