Feature Flags Architect

Feature Flags Architect

End-to-end feature flag design, rollout, and lifecycle management. Covers flag taxonomy (release vs ops vs experiment vs permission), gradual rollout patterns with blast-radius math, kill-switch runbooks, governance (who can flip what), and the flag-debt cleanup loop that keeps a codebase from drowning in stale flags.

This skill is provider-agnostic: the patterns work whether you run LaunchDarkly, Statsig, Unleash, Flagsmith, ConfigCat, GrowthBook, OpenFeature, or a homegrown system backed by Redis/DynamoDB/Postgres.

Core Capabilities

• Flag taxonomy — classify every flag as one of four types (release, ops, experiment, permission); the type sets lifetime, who flips it, and auto-expiry.
• Rollout ramps — dogfood → canary → 100% schedules with per-step blast-radius math and ramp templates by change type.
• Kill switches — ops-flag pattern with fail-open/closed decisions, runbooks, and alerting for risky dependencies or code paths.
• Governance — role-based who-can-flip-what matrix plus audit-log/retention requirements, mappable onto any flag system.
• Flag debt cleanup — quarterly inventory → classify → decide → execute → measure loop to keep flag count flat or shrinking.
• End-to-end workflows — add a release flag, build a kill switch, audit flag debt, flag-based rollback after a bad release.

Flag taxonomy — the four types

Every flag belongs to exactly one of these four types. The type determines the lifecycle, who can flip it, and whether it should auto-expire. Mixing types in one flag is a root cause of flag debt.

| Type | Purpose | Lifetime | Who flips | Auto-expire? |

|------|---------|----------|-----------|--------------|

| Release | Decouple deploy from release. Ship code dark, ramp to users. | Days to weeks | Engineer who owns the feature | Yes — remove after 100% rollout + 1 release |

| Ops | Kill switches, circuit breakers, throttles. Turn off risky behavior fast. | Permanent or long-lived | Oncall / SRE / platform team | No — but review quarterly |

| Experiment | A/B test, multi-arm bandit, hold-out group. Measure causal impact. | Weeks to months (test duration) | Product / data / growth | Yes — remove after winner is shipped |

| Permission | Entitle users to features based on plan, role, beta-list. | Permanent | Product / billing | No — but consolidate into entitlement system |

Decision rule when adding a flag: name the type. If you can't, the flag shouldn't exist yet — clarify intent first.

When to Use

• Designing a flag system from scratch — start with the flag taxonomy.
• Planning a risky release (DB migration, payment-provider swap, framework upgrade) — use the rollout ramp + kill switch.
• Auditing a codebase with hundreds of growing flags — use flag debt cleanup + scripts/flag_audit.py.
• Setting up an A/B test or hold-out — covers the flag side; pair with engineering/experiment-design for statistics.
• Building a kill switch for a third-party dependency outage — use the kill switch runbook generator.
• Defining who in the org can flip production flags — use the governance matrix.
• Building entitlements / paid-tier gating — use this for flag mechanics; business-growth/paywall-upgrade-cro for the UX.

Clarify First

Before designing or operating flags, confirm these inputs. If any is unknown or vague, ASK — do not assume:

• [ ] Flag type — release, ops, experiment, or permission (sets the lifecycle, who can flip it, and auto-expiry — the root decision)
• [ ] Task — design a taxonomy, simulate a rollout ramp, generate a kill-switch runbook, or audit flag debt (selects flag_audit.py vs rollout_simulator.py vs kill_switch_runbook.py)
• [ ] Blast radius / population — user count and ramp profile, or the dependency a kill switch guards (drives --users/--profile and the runbook content)

Stop rule: ask only the 2-3 that most change the output. If the user says "just draft it," proceed and list your assumptions at the top of the artifact.

Tools

| Tool | Purpose | Command |

|------|---------|---------|

| flag_audit.py | Scan a codebase for flag references, age, classification, and recommended action (optionally cross-reference a control-plane export) | python scripts/flag_audit.py --path . --format markdown |

| rollout_simulator.py | Model a rollout: per-step blast radius, time-to-detect, recommended schedule | python scripts/rollout_simulator.py --users 500000 --profile standard |

| kill_switch_runbook.py | Generate a kill-switch runbook (default state, flip procedure, validation, escalation) | python scripts/kill_switch_runbook.py --flag ops.recs.kill_switch --feature Recommendations --dependency recs-svc |

All scripts: standard library only, argparse CLI, JSON + human-readable output. Run --help for full usage.

References

Load the reference that matches the task — keep this file lean and pull detail on demand:

• references/flag-types-and-patterns.md — the four flag types in depth, code patterns per type, evaluation-context schema, naming conventions, server-vs-client trade-offs, and storage models. Read when designing a flag system or writing the gating code.
• references/operations-governance-and-workflows.md — the standard ramp table, blast-radius math, kill-switch design, the governance matrix + audit-log requirements, the flag-debt cleanup loop, all four end-to-end workflows, the anti-patterns list, and the tooling input/output reference. Read when running a rollout, defining governance, or executing a workflow.
• references/rollout-and-kill-switch-playbook.md — rollout decision tree, ramp templates by change type, cohort/segment selection, kill-switch design, and monitoring/alerting hookup. Read when planning a specific ramp or wiring kill-switch alerting.
• references/flag-debt-and-cleanup.md — what flag debt costs, the cleanup cadence, dead-code detection, safe removal procedures, PR templates, and governance for flag count. Read when paying down stale flags.

Scope & Limitations

This skill covers: flag taxonomy and lifecycle, rollout ramps with blast-radius math, kill-switch design and runbooks, governance/audit requirements, and flag-debt cleanup — provider-agnostic across LaunchDarkly, Statsig, Unleash, Flagsmith, ConfigCat, GrowthBook, OpenFeature, and homegrown systems.

This skill does NOT cover: the statistical design of A/B tests (pair with product-team/experiment-design), the paywall/upgrade UX for entitlements (business-growth/paywall-upgrade-cro), or the metric instrumentation needed to make ramp decisions (engineering/observability-designer).

Related skills

• engineering/observability-designer — wire the metrics needed to make ramp decisions
• engineering/incident-commander — flag-based rollback during incidents
• engineering/chaos-engineering — verify kill switches actually work under fault injection
• product-team/experiment-design (if available) — statistical design of A/B tests behind flags