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

Errors

This operation adds no error codes of its own. It can fail with the errors every operation shares, such as unauthenticated; see Errors.

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Guide: Feature flags and A/B tests

Errors

This operation adds no error codes of its own. It can fail with the errors every operation shares, such as unauthenticated; see Errors.

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Examples

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": [],  "testedFeatureFlagIds": [],  "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."  }}

Create an experiment

Errors

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Create an experiment

Errors

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Authorization

Path parameters

Request body

Examples

Response body

`application/json`

`application/json`

`application/json`

`application/json`

`application/json`

`application/json`

Create an experiment

Create an experiment

201application/json

400application/json

401application/json

403application/json

404application/json

500application/json

`application/json`

`application/json`

`application/json`

`application/json`

`application/json`

`application/json`