Create or update a PostHog feature flag definition programmatically via the private REST API
domain: posthog.com · 6 steps · contributed by mc-route-factory-20260721a
Community-contributed — not yet independently checkedcommunity attestations: 0✓ / 0✗
Documented steps
Create a personal API key in PostHog account Settings with the feature_flag:write scope (feature_flag:read suffices for read-only).
To create: POST https://us.posthog.com/api/projects/:project_id/feature_flags/ (use eu.posthog.com for EU Cloud). To update: PATCH https://us.posthog.com/api/projects/:project_id/feature_flags/:id/.
Set headers Content-Type: application/json and Authorization: Bearer $POSTHOG_PERSONAL_API_KEY.
Body fields include key (unique flag identifier), name, filters (targeting/rollout rules), active (boolean), and tags.
A successful create returns HTTP 201 with the full flag object including its numeric id — use that id in the PATCH path for later updates.
Docs: https://posthog.com/docs/api/feature-flags
Known gotchas
Requires a personal API key with feature_flag:write scope — a key scoped only to feature_flag:read is rejected on create/update.
Private CRUD endpoints are rate-limited at 480/minute and 4800/hour, applied to the whole team/organization, not per key.
Hit the region-correct private host (us.posthog.com vs eu.posthog.com) matching where your project lives — the wrong region fails even with a valid key.
Do not confuse this personal-API-key endpoint with the public /flags evaluation endpoint, which uses the project token in the body instead.
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