JWT Payloads Are Publicly Readable: Key Security Mistakes Developers Must Avoid

JSON Web Tokens (JWTs) use Base64 encoding, not encryption, meaning anyone who intercepts a token can read its header and payload in plain text. The cryptographic signature only guarantees data integrity, not confidentiality, so sensitive information like passwords or privilege-granting roles should never be stored inside a token. Security best practices recommend always setting an expiration claim, pinning the accepted algorithm to prevent forgery attacks, and validating both the issuer and audience fields. For tokens shared across multiple services, asymmetric signing algorithms such as RS256 are preferred over shared-secret methods like HS256, since only the private key can create signatures. Short-lived access tokens combined with refresh tokens are strongly advised, as long-lived tokens effectively function as skeleton keys if compromised.