Create an experiment
Creates a draft experiment with a control and one other arm at 50% each, and the feature flag that will assign end users to them.
Set its arms with PUT .../variants and its goal (primaryMetricEventName) with PATCH before starting it: the default goal, purchase_completed, is an event Voidhash never sends, so an experiment left on it records no conversions.
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.
Request body
application/json
TypeScript definitions
Use the request body type in TypeScript.
The experiment's name.
1 <= lengthExamples
curl -X POST "https://api.voidhash.com/api/v1/projects/proj_tz4a98xxat96iws9zmbrgj3a/experiments" \ -H "Authorization: Bearer vh_sk_..." \ -H "Content-Type: application/json" \ -d '{ "name": "Onboarding paywall pricing" }'{ "id": "exp_c6v8b3n5q0w2e7h7d2k9m4x1", "projectId": "proj_tz4a98xxat96iws9zmbrgj3a", "name": "Onboarding paywall pricing", "description": null, "hypothesis": null, "status": "draft", "primaryMetricEventName": "purchase_completed", "secondaryMetricEventNames": [], "paywallLocationIds": [], "winningVariantId": null, "featureFlagId": "ff_k9m4x1c6v8b3n5q0w2e7h7d2", "isArchived": false, "startedAt": null, "endedAt": null, "createdAt": "2026-02-27T15:20:00.000Z", "updatedAt": "2026-02-27T15:20:00.000Z"}{ "error": { "type": "invalid_request", "code": "invalid_body", "message": "The request body is invalid: Missing key\n at [\"name\"]" }}{ "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": "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
Errors
This operation adds no error codes of its own. It can fail with the errors every operation shares, such as unauthenticated; see Errors.
More in Experiments
- List experiments
GET - Retrieve an experiment
GET - Update an experiment
PATCH - 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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