Create a feature flag

Creates a flag, switched off and serving nobody in production, with test following production.

A string, number or json flag takes variants whose values match its type; a boolean flag has none.

Errors

Status	`type`	`code`	When
400	`invalid_request`	`invalid_variants`	When they do not fit.
409	`conflict`	`feature_flag_key_taken`	When another flag, archived or not, uses the key.

It can also fail with the errors every operation shares, such as unauthenticated; see Errors.

Errors

Status	`type`	`code`	When
400	`invalid_request`	`invalid_variants`	When they do not fit.
409	`conflict`	`feature_flag_key_taken`	When another flag, archived or not, uses the key.

It can also fail with the errors every operation shares, such as unauthenticated; see Errors.

Request body

application/json

TypeScript definitions

Use the request body type in TypeScript.

key*string

The flag's key, unique in the project; SDKs ask for the flag by it.

Length1 <= length

description?|

What the flag controls.

type?|

What the flag evaluates to; defaults to boolean. It cannot change afterwards.

variants?array<>|

The values a string, number or json flag can evaluate to, at least one; traffic splits evenly between them. A boolean flag takes none.

Examples

curl -X POST "https://api.voidhash.com/api/v1/projects/proj_tz4a98xxat96iws9zmbrgj3a/feature-flags" \  -H "Authorization: Bearer vh_sk_..." \  -H "Content-Type: application/json" \  -d '{    "key": "checkout-headline",    "description": "The headline of the checkout screen.",    "type": "string",    "variants": [      {        "label": "Plain",        "value": "Go Pro"      },      {        "label": "Benefit",        "value": "Unlock every workout"      }    ]  }'

{  "id": "ff_d2k9m4x1c6v8b3n5q0w2e7h7",  "projectId": "proj_tz4a98xxat96iws9zmbrgj3a",  "key": "checkout-headline",  "description": "The headline of the checkout screen.",  "type": "string",  "environments": {    "production": {      "isEnabled": false,      "overrides": [],      "rules": [],      "fallthrough": {        "rolloutPercentage": 0,        "variantKey": null      }    },    "test": null  },  "isArchived": false,  "experimentId": null,  "createdAt": "2026-03-12T10:00:00.000Z",  "updatedAt": "2026-03-12T10:00:00.000Z"}

{  "error": {    "type": "invalid_request",    "code": "invalid_variants",    "message": "Boolean feature flags cannot have variants",    "param": "variants"  }}

{  "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": "feature_flag_key_taken",    "message": "Another feature flag in this project, archived or not, already uses the key \"new-onboarding\".",    "param": "key"  }}

{  "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."  }}

Errors

More in Feature flags

Create a feature flag

Errors

More in Feature flags

Authorization

Path parameters

Request body

Examples

Response body

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Create a feature flag

Create a feature flag

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400application/json

401application/json

403application/json

404application/json

409application/json

500application/json

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