JWT Decode — Free Online Tool

A JWT decoder is a tool that parses JSON Web Tokens to reveal the header, payload claims, and signature without needing a secret key. SWEDevTools: Prism provides a free, local-first JWT decoder that runs entirely in your browser—no tokens are ever sent to a server—making it safe for inspecting production access tokens, debugging OAuth flows, and troubleshooting authentication errors.

Features

• Header + payload extraction: View the protected header (algorithm, key ID) and claims payload in a single structured output.
• Payload-only mode: Extract just the claims object when you only need to inspect scopes, roles, or custom claims without the header noise.
• Local-first privacy: Tokens never leave your device. Decode production JWTs safely without uploading them to jwt.io or other hosted services.
• Works offline as a PWA: Install SWEDevTools: Prism and decode JWTs without an internet connection—essential for on-call debugging in restricted environments.
• No signup required: Decode tokens instantly with zero account creation, no email verification, and no usage limits.
• Pipeline chaining support: Chain decoded claims into JSON formatters, diff tools, and validators in a single pipeline workflow.

Frequently Asked Questions

Is the JWT decoder free?

Yes, the SWEDevTools: Prism JWT decoder is completely free with no signup, no ads, and no usage limits.

Does the JWT decoder work offline?

Yes. SWEDevTools: Prism is a PWA that works without an internet connection once installed on your device.

Is my data safe when decoding JWTs?

Yes. All decoding happens locally in your browser. No tokens are ever uploaded to a server, making it safe for production tokens containing sensitive claims.

Does this verify the JWT signature?

No. This tool is for decoding and inspection only. Signature verification requires the correct secret key or public key and should be performed in your application’s authentication logic.

Is decoding a JWT dangerous?

Decoding is just parsing Base64URL-encoded JSON—it does not reveal secrets. The real risk is sharing the raw token. SWEDevTools: Prism keeps everything local so your token is never exposed.

What does the "alg" field in a JWT header mean?

The "alg" (algorithm) field specifies how the token was signed, such as HS256 (HMAC-SHA256), RS256 (RSA-SHA256), or ES256 (ECDSA). It tells the verifier which algorithm to use for signature validation.

Why do I see exp, nbf, and iat claims?

These are standard JWT timestamp claims: exp (expiration time), nbf (not valid before), and iat (issued at). They control token validity windows. Inspect them when troubleshooting "token expired" errors or clock-skew issues.

Why does my JWT fail to decode?

The token may not have exactly three dot-separated parts, or the header/payload may contain invalid Base64URL encoding. Verify the token format and ensure no whitespace or line breaks were introduced during copy-paste.

How is this different from jwt.io?

jwt.io uploads your token to a hosted service for decoding. SWEDevTools: Prism decodes entirely in your browser with zero network requests, provides pipeline chaining with other dev tools, and works offline as an installable PWA.

Can I decode JWTs from different identity providers?

Yes. The decoder works with any standard JWT regardless of issuer—Auth0, Okta, AWS Cognito, Azure AD, Firebase, Keycloak, and custom implementations all produce standard three-part tokens.

Is Prism a good alternative to jwt.io?

Yes. The key difference is privacy: jwt.io sends your token to their server for decoding, while SWEDevTools: Prism decodes entirely in your browser — your tokens never leave your device. Prism also works offline as a PWA, requires no signup, and supports pipeline chaining into JSON formatters, diff tools, and validators.

What happened to smalldev.tools?

smalldev.tools is no longer available. Prism by SWEDevTools offers the same developer tools and more, with offline support, pipeline chaining, and completely free usage — no signup required.