JWT Decoder — Free Online Tool

What Is JWT Decoder?

A free online JWT (JSON Web Token) decoder. Paste any JWT to instantly view its decoded header and payload as formatted JSON with syntax highlighting. Check expiration status, issuer, and claims. Note: this tool decodes but does NOT verify signatures.

JSON Web Tokens (JWTs) are a compact, URL-safe token format used extensively in modern authentication systems, API authorization, and single sign-on implementations. JWT Decoder lets you paste any JWT and instantly inspect its decoded header and payload, making it easier to debug authentication flows and understand token contents.

When you paste a JWT, the tool immediately splits it into its three components — header, payload, and signature — and decodes the base64url-encoded header and payload into formatted JSON. The header shows the signing algorithm (like HS256 or RS256) and token type. The payload reveals all claims including standard ones like iss (issuer), sub (subject), aud (audience), exp (expiration time), nbf (not before), iat (issued at), and any custom claims the issuer has included.

The expiration status is highlighted with a clear indicator: valid (token has not expired), expired (past the expiration time), or not yet valid (before the nbf time). This is particularly useful during development when you need to quickly verify whether a test token has expired or if the time-based claims are set correctly.

A critical distinction: this tool decodes but does NOT verify signatures. Decoding a JWT is trivially easy — the header and payload are just base64url-encoded JSON that anyone can read. The signature is what ensures the token has not been tampered with. Without verification, you should never trust decoded claims from an untrusted source. For signature verification, you need the signing key and appropriate server-side logic.

Real-World Use Cases for JWT Decoder

Debugging an Authentication Token

Your API is returning 401 errors and you suspect the JWT is expired. Paste the token into the decoder and look at the exp claim. The tool shows "Expired" if the timestamp is in the past, confirming the issue. Check the iat claim to see when the token was issued and debug your token refresh logic.

Inspecting OAuth ID Tokens

An OAuth provider returns an id_token during login. Paste it into the decoder to inspect the iss (issuer URL), sub (user identifier), aud (client ID), and any custom claims like email or name. This is useful for verifying that the token comes from the expected issuer and contains the expected audience.

Checking Claims in a Development Token

During local development, you generate test JWTs with custom claims for feature testing. Paste the token to verify all claims are set correctly — check that the sub, roles, and permissions claims have the expected values before testing your authorization middleware.

Why Use JWT Decoder?

Instant base64url decoding of header and payload
Syntax-highlighted JSON output
Expiration status: valid, expired, or not yet valid
Displays iat, exp, nbf, iss, sub claims

How to Use JWT Decoder — Step by Step

Paste your JWT token into the input field.

The header and payload are decoded instantly.

Review claims, expiration status, and issuer.

Copy any decoded section as needed.

Who Is JWT Decoder Best For?

API debugging
auth troubleshooting
token inspection
OAuth development

Pro Tips for JWT Decoder

1JWT header and payload are base64url-encoded, NOT encrypted. Anyone who has the token can read the contents. Never put sensitive information (passwords, secrets, PII) in JWT claims.
2Always check the "typ" (type) header. A JWT should have typ: "JWT". This helps you distinguish JWTs from other JOSE objects like JWE or JWS.
3The "exp" claim is the most commonly checked validation. Ensure your server checks exp, nbf, and iss at minimum. Skipping these checks is a common security vulnerability in JWT implementations.
4Use https://jwt.io or this decoder locally for debugging, but implement proper signature verification on the server side using your authentication library. Never trust decoded claims without verifying the signature.

JWT Decoder — Frequently Asked Questions

Does this tool verify JWT signatures?

No. This tool only decodes the header and payload. It does not verify the cryptographic signature. Never trust decoded JWT claims without proper server-side signature verification.

What claims does the decoder show?

It highlights standard claims: iss (issuer), sub (subject), aud (audience), exp (expiration), nbf (not before), and iat (issued at), along with any custom claims in the payload.

Can I use these tools with sensitive/proprietary data?

Absolutely. All processing runs locally in your browser with zero server uploads. This makes these tools safe for proprietary code, internal API keys, and confidential data.

Do these tools work offline?

Yes, once the page has loaded, most developer tools continue functioning without an internet connection. This makes them ideal for air-gapped environments or travel.

What browsers are supported?

All modern browsers are supported: Chrome, Firefox, Safari, and Edge. Internet Explorer is not supported. The tools leverage modern JavaScript APIs like Web Crypto, TextEncoder, and BigInt.

Ready to Use JWT Decoder?

Free online tool — works in your browser, no sign-up required. Start using it right now.

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