Developer Privacy guide

How to Check a JWT for Sensitive Data

A signed JWT is usually readable by anyone who receives it. A signature protects integrity; it does not normally hide the payload.

Encoding is not encryption

The header and payload of a common signed JWT are base64url encoded. They can usually be decoded without the signing key. The signature allows a verifier to detect changes, but it does not make the claims confidential.

Encrypted JWTs, often called JWE, are different. A simple three-part decoder does not inspect encrypted content.

Review identity and authorization claims

Look for sub, email, name, phone, user_id, account_id, tenant, organization, roles, permissions, groups, issuer, audience, and custom application fields.

Even values that look random may map directly to a user or customer record in your system.

Do not share live tokens

A token may grant access until it expires or is revoked. Redacting only the payload after posting the complete token does not remove the access risk.

Use a fabricated token or share only a cleaned decoded payload when the claim structure is the issue.

Separate privacy review from validation

A local decoder does not verify the signature, issuer, audience, expiry, revocation, key rotation, or server-side authorization rules.

Use the official application or server library for validation. Use the privacy checker only to understand what the readable token reveals.

Final review checklist

  • No live production token is shared
  • Custom claims reviewed
  • Identity and permission claims masked
  • Exposed tokens revoked
  • Server-side validation used for trust decisions

Written and maintained by Imran Gul

Imran is a web developer who builds browser-based tools and maintains Privacy Toolbox. These guides explain practical workflows and limitations; they are not legal, medical, compliance, or security advice.

Read the testing methodology
Apply the guide

Related browser tools

Use local processing for the first pass, then review the output before sharing.

Choose the tool that matches your content

Clean text, logs, JSON, CSV data, screenshots, image metadata, links, or file hashes in your browser.

Browse tools