Feature Flag Management is the capability that decouples deploying code from releasing it: create a flag, target it to a cohort, roll it out, retire it. The catalog maps 37 API surfaces from 18 providers onto it, seven of them rated strong or better. Read the list by who sells flags and who merely has them, and the scores run backwards.
Same job, very different shapes
| Provider | How it exposes flags | Kin Score |
|---|---|---|
| Optimizely | Features, Flags, Rulesets, Rules and Ship Rules as separate APIs | 80.8, exemplar |
| Medusa | One Feature Flags API: admin users view the flags | 65.2, strong |
| Frontegg | One Feature Flags API, 2 operations | 65.0, strong |
| WorkOS | Flags, flag targets, and flags scoped to organizations and to users | 59.6, strong |
| GitLab CI | feature_flags, features, and an unleash endpoint |
45.1, developing |
| Unleash | 10 surfaces: Archive, Client, Context, Dependencies and more | 45.3, developing |
| GrowthBook | Features and feature revisions, each in v1 and v2 | 32.9, thin |
| Convert | Features | 27.1, thin |
The shapes tell you what each company thinks a flag is. For Medusa a flag is a configuration switch inside a commerce engine, and the API lets an admin see it. For Frontegg, an identity platform, flags ride alongside entitlements. Optimizely splits the job into the flag, the ruleset that targets it and the rule that ships it, which is the most complete decomposition on the page, and it leads at 80.8.
Unleash is the purest flag product on the list: an open-source feature management platform whose catalog runs to 37 API pages covering strategies, segments, a playground, dependencies between flags, and an unknown-flags report. It maps 10 surfaces onto this capability, more than anyone else, and scores 45.3. GrowthBook, open-source flagging and experimentation, scores 32.9. Its v2 Features API changed the rule model, returning rules as one top-level array scoped by environment instead of bucketed per environment, and both versions stay published side by side.
What the scores are measuring
The Kin Score does not measure how good a flag system is. It measures the public API record around it: contracts, governance, operational signals, access clarity. A company that sells flags as its product is often a smaller open-source project with a large, fast-moving API and thin surrounding artifacts. A company that bolts flags onto a mature platform inherits the platform’s record. That is why Frontegg and Medusa outscore the specialists here, and it is worth knowing before anyone reads this page as a vendor ranking.
Agent Readiness runs the other way for GrowthBook: 47.0 against a Kin Score of 32.9. A small, consistent contract is most of what an agent needs to flip a flag.
Who the page misses
The capability page is also missing the category’s best records. LaunchDarkly scores 77.8, exemplar, and publishes a Feature Flags API. Flagsmith scores 77.9 with Features, Segments and Identities APIs. Statsig scores 76.9 with a Feature Gates API. DevCycle publishes an OpenFeature Remote Evaluation API, the vendor-neutral shape this capability should converge on. None of the four is mapped. That is a gap in our capability mapping, not in their surfaces.
Takeaway
For flag specialists, the move is the surrounding record: governance, changelogs, deprecation notes for the v1 surfaces still published. For us, it is mapping LaunchDarkly, Flagsmith, Statsig and DevCycle so the page compares the companies that actually sell the job.
See the capability at apis.io/capabilities/feature-flag-management/.