[Home](./index.md) > [@digitalpersona/core](./core.md) > [JWT](./core.jwt.md) > [errors](./core.jwt.errors.md) ## JWT.errors() method Validates the JSON Web Token and returns a collection of detected validation errors. Signature: ```typescript static errors(jwt: JSONWebToken): Error[] | null; ``` ## Parameters | Parameter | Type | Description | | --- | --- | --- | | jwt | JSONWebToken | a JSON Web Token. | Returns: `Error[] | null` an array of errors found, or `null` if the token is valid. ## Remarks Only client-side checks are performed, no signature validation. The token's claims must satisfy following expression: `iat <= nbf < now < exp` where `iat` is time when the token was issued, `nbf` is a time when the token becomes valid, `exp` is a token expiration time, `now` is current time. Following errors may be returned: \* 'JWT.Error.IssueTimeLaterThanNotBefore' if `iat > nbf`, \* 'JWT.Error.NotEffectiveYet' when `now < nbf`, \* 'JWT.Error.Expired' when `now >= exp`.