Update an experiment
Renames an experiment or changes its description, hypothesis or metrics.
Set primaryMetricEventName explicitly, such as to $subscription.created or $purchase.completed: the default, purchase_completed, is never sent by Voidhash.
Guide: Feature flags and A/B tests
A project secret key: vh_sk_... for production, vh_sk_test_... for test. Keep it on your servers.
In: header
Path parameters
The project's id, proj_.... A secret key works only in the project it belongs to.
The experiment's id, exp_....
Request body
application/json
TypeScript definitions
Use the request body type in TypeScript.
The new name.
The new description; null clears it.
The new hypothesis; null clears it.
The event that counts as a conversion, such as $subscription.created (a new subscription, trial starts included) or $purchase.completed (any purchase, one-time and consumable ones included). Null counts purchase_completed, which Voidhash itself never sends, so set it explicitly. Only while the experiment is a draft.
Further events to watch, replacing the ones set before. Only while the experiment is a draft.
Examples
curl -X PATCH "https://api.voidhash.com/api/v1/projects/proj_tz4a98xxat96iws9zmbrgj3a/experiments/exp_c6v8b3n5q0w2e7h7d2k9m4x1" \ -H "Authorization: Bearer vh_sk_..." \ -H "Content-Type: application/json" \ -d '{ "description": "The monthly-first paywall against the annual-first one after onboarding.", "hypothesis": "Leading with the annual plan brings more new subscriptions.", "primaryMetricEventName": "$subscription.created" }'{ "id": "exp_c6v8b3n5q0w2e7h7d2k9m4x1", "projectId": "proj_tz4a98xxat96iws9zmbrgj3a", "name": "Onboarding paywall pricing", "description": "The monthly-first paywall against the annual-first one after onboarding.", "hypothesis": "Leading with the annual plan brings more new subscriptions.", "status": "draft", "primaryMetricEventName": "$subscription.created", "secondaryMetricEventNames": [], "paywallLocationIds": [ "pw_loc_m4x1c6v8b3n5q0w2e7h7d2k9" ], "winningVariantId": null, "featureFlagId": "ff_k9m4x1c6v8b3n5q0w2e7h7d2", "isArchived": false, "startedAt": null, "endedAt": null, "createdAt": "2026-02-27T15:20:00.000Z", "updatedAt": "2026-02-27T15:31:00.000Z"}{ "error": { "type": "invalid_request", "code": "invalid_body", "message": "The request body is invalid: Expected object" }}{ "error": { "type": "unauthenticated", "code": "invalid_api_key", "message": "This secret key is not valid." }}{ "error": { "type": "permission_denied", "code": "permission_denied", "message": "Insufficient permissions." }}{ "error": { "type": "not_found", "code": "project_not_found", "message": "There is no project proj_tz4a98xxat96iws9zmbrgj3a, or this credential cannot use it.", "param": "projectId" }}{ "error": { "type": "conflict", "code": "experiment_metrics_locked", "message": "Experiment exp_c6v8b3n5q0w2e7h7d2k9m4x1 has started, so what counts as a conversion can no longer change." }}{ "error": { "type": "internal", "code": "internal_error", "message": "Something went wrong on our side. Try again, and contact support with the Request-Id header if it keeps failing." }}Response body
application/json
application/json
application/json
application/json
application/json
application/json
application/json
Errors
| Status | type | code | When |
|---|---|---|---|
| 409 | conflict | experiment_metrics_locked | When changing a metric after it left draft; sending the metrics it already has is fine. |
It can also fail with the errors every operation shares, such as unauthenticated; see Errors.
More in Experiments
- List experiments
GET - Create an experiment
POST - Retrieve an experiment
GET - Archive an experiment
POST - Unarchive an experiment
POST - Start an experiment
POST - Pause an experiment
POST - Conclude an experiment
POST - List an experiment's arms
GET - Replace an experiment's arms
PUT - Retrieve an experiment's results
GET
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