> For the complete documentation index, see [llms.txt](https://docs.defguard.net/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.defguard.net/for-developers/rest-api/core/system/check-whether-an-email-address-or-username-is-already-taken.md).

# Check whether an email address or username is already taken

```json
{"openapi":"3.1.0","info":{"title":"defguard Core API","version":"2.0.3"},"tags":[{"name":"system","description":"Health check, instance info and other utility endpoints."}],"security":[{"cookie":[]},{"api_token":[]}],"components":{"securitySchemes":{"cookie":{"type":"apiKey","in":"cookie","name":"defguard_session"},"api_token":{"type":"http","scheme":"bearer"}},"schemas":{"CheckResource":{"type":"string","enum":["email","username"]},"ApiErrorResponse":{"type":"object","description":"Body returned with error responses.","required":["msg"],"properties":{"code":{"type":["string","null"],"description":"Machine-readable error code, returned for selected errors."},"msg":{"type":"string","description":"Human-readable error message."}}}}},"paths":{"/api/v1/reserved":{"get":{"tags":["system"],"summary":"Check whether an email address or username is already taken","operationId":"check_reserved","parameters":[{"name":"resource","in":"query","description":"Type of the checked value: `email` or `username`.","required":true,"schema":{"$ref":"#/components/schemas/CheckResource"}},{"name":"value","in":"query","description":"Value to check.","required":true,"schema":{"type":"string"}}],"responses":{"200":{"description":"Availability of the value.","content":{"application/json":{"schema":{"type":"object"}}}},"401":{"description":"Session is missing or invalid.","content":{"application/json":{"schema":{"$ref":"#/components/schemas/ApiErrorResponse"}}}},"403":{"description":"Requires admin privileges.","content":{"application/json":{"schema":{"$ref":"#/components/schemas/ApiErrorResponse"}}}},"409":{"description":"The value is already taken.","content":{"application/json":{"schema":{"$ref":"#/components/schemas/ApiErrorResponse"}}}},"500":{"description":"Unable to check the value.","content":{"application/json":{"schema":{"$ref":"#/components/schemas/ApiErrorResponse"}}}}}}}}}
```