The Security Risk of Online JWT Decoders (And Why Ours is Different)

Pasting your JWT into a third-party "decode JWT" website can send your token to their servers. That’s a real privacy and security risk. This post explains why, and how a decoder that runs entirely in your browser keeps you safe.

What Happens When You Use an Online JWT Decoder?

Many "online JWT decoder" tools work like this:

1. You paste your token into their website.
2. Their server receives the token (often over HTTPS, but it still reaches their backend).
3. The server decodes the token and returns header and payload to your browser.

So your JWT—which may contain session IDs, user identifiers, or other sensitive claims—is now on their infrastructure. They can log it, store it, or use it. Even if they claim not to, you have no way to verify that, and a breach or misuse would expose your tokens.

Why This Matters

• Session hijacking: A stolen JWT can be used to impersonate you if your app relies on it for auth.
• Data exposure: JWTs often contain PII or internal IDs; sending them to a third party can violate privacy expectations or policy.
• Compliance: Handling tokens on external servers can conflict with data-residency or "no third-party processing" requirements.

You should treat every JWT as sensitive. The safest approach is to never send it to a server you don’t control.

How Our JWT Decoder is Different

Our JWT Decoder runs entirely in your browser. When you paste a token:

• Nothing is sent to our servers. Decoding (base64 and JSON parsing) happens in JavaScript on your device.
• We don’t store or log your token. We have no backend that receives it.
• You stay in control. Your token never leaves your machine.

That’s the "local-only" model: the tool is just a web page that does the work locally, like a calculator. No round-trip, no third-party access to your data.

What You Can Do Right Now

1. Stop using random online JWT decoders for real tokens. If you need to inspect a token, use a decoder that runs in the browser and doesn’t send the token to a server.
2. Use our JWT Decoder for debugging and inspection: Try our JWT Decoder. Same decoding, zero server exposure.
3. Check your privacy policy (and your provider’s): we document how our tools work in our Privacy Policy.

Decode JWTs when you need to—but keep them off third-party servers. Use a local-only decoder and keep your tokens in your hands.