What is a JWT debugger?

A JWT debugger is a tool that decodes JSON Web Tokens into readable header and payload JSON, allowing developers to inspect authentication claims, expiration timestamps, and token structure during development and troubleshooting.

Is it safe to paste production JWT tokens into an online debugger?

Only use client-side debuggers like ScanSuite that process tokens locally in your browser. Avoid services that send tokens to remote servers, as decoded payloads often contain sensitive user data and credentials.

What are the three parts of a JWT?

A JWT consists of a header (algorithm and token type), a payload (claims and metadata), and a signature (cryptographic proof of integrity). The three Base64URL-encoded segments are separated by dots.

Can a JWT debugger verify token signatures?

A debugger displays the signature segment but full verification requires the signing secret (for HMAC) or public key (for RSA/ECDSA) and should always be performed server-side in production applications.

What is the difference between decoding and validating a JWT?

Decoding reveals the header and payload contents by reversing Base64URL encoding. Validating additionally verifies the cryptographic signature, checks expiration, and confirms issuer and audience claims match expected values.

What does the exp claim mean in a JWT?

The exp (expiration time) claim is a NumericDate timestamp indicating when the token becomes invalid. Validators must reject tokens where the current time exceeds the exp value.

What is the alg:none vulnerability?

The alg:none attack occurs when an attacker modifies the JWT header algorithm to none, removing signature verification. Servers must whitelist allowed algorithms and never accept unsigned tokens in production.

How do I decode a JWT in the browser without a tool?

Split the token on dots, Base64URL-decode the first two segments, and parse the result as JSON. ScanSuite automates this process with formatting, syntax highlighting, and claim inspection.

What is the difference between an access token and an ID token?

Access tokens authorize API requests and contain scopes and permissions. ID tokens authenticate the user's identity and contain profile claims like name and email. Both use JWT format but serve different purposes in OAuth 2.0 flows.

Why does my JWT have five segments instead of three?

A five-segment token is a JWE (JSON Web Encryption) token, which encrypts the payload for confidentiality. Standard JWT debuggers decode three-segment JWS (JSON Web Signature) tokens only.

What registered claims should I always include in JWTs?

Production JWTs should include iss (issuer), sub (subject), aud (audience), exp (expiration), and iat (issued at) claims at minimum. Add jti (JWT ID) for replay prevention in high-security contexts.

How long should JWT access tokens be valid?

Industry best practice recommends short-lived access tokens of 5 to 15 minutes, combined with refresh tokens for session continuity. Long-lived tokens increase the impact of token theft or leakage.

Can I edit JWT claims in the debugger?

Yes. ScanSuite allows in-place editing of header and payload JSON for local development testing. Note that modifying claims invalidates the original signature unless you re-sign with the correct secret or private key.

What is Base64URL encoding?

Base64URL is a URL-safe variant of Base64 encoding used in JWTs. It replaces + with -, / with _, and omits padding equals signs, making tokens safe for use in HTTP headers and URL query parameters.

How do refresh tokens differ from access tokens?

Refresh tokens are long-lived credentials used solely to obtain new access tokens from the authorization server. They should be stored securely, rotated on each use, and never sent to resource APIs.

What is a JWKS endpoint?

A JSON Web Key Set (JWKS) endpoint publishes public keys used to verify RS256 and ES256 JWT signatures. OAuth providers like Auth0 and Okta expose JWKS URLs for automatic key rotation support.

Does ScanSuite store or log my JWT tokens?

No. All decoding happens entirely in your browser using client-side JavaScript. Tokens are never transmitted to ScanSuite servers, logged, or persisted in any storage.

What causes Invalid JWT format errors?

Common causes include missing dot separators, extra whitespace, truncated tokens, standard Base64 instead of Base64URL encoding, or attempting to decode a JWE five-segment encrypted token with a JWS decoder.

Should I use HS256 or RS256 for my application?

Use RS256 (asymmetric) when multiple services verify tokens or when using third-party identity providers with JWKS. Use HS256 (symmetric) only in trusted monolithic environments with strong shared secrets managed via secure vaults.

How do I check if my JWT has expired?

Decode the token and compare the exp claim (Unix timestamp) against the current time. ScanSuite highlights expiration claims automatically. Use the Timestamp Converter to translate exp values into readable dates.

Free Online JWT Debugger & Decoder Tool

A JWT debugger is a web-based tool that decodes JSON Web Tokens (JWTs) into human-readable header and payload JSON objects, displays registered and private claims, highlights expiration and not-before timestamps, and helps developers inspect authentication and authorization tokens without sending sensitive credentials to remote servers.

Paste your JWT string into ScanSuite's free JWT debugger to instantly decode the Base64URL-encoded header and payload sections, view formatted JSON claims including exp, iat, sub, and aud, inspect the signature segment, and copy individual sections for API debugging — all processing happens locally in your browser.

JSON Web Tokens (JWTs) have become the de facto standard for stateless authentication and authorization in modern web applications, single-page apps, and microservice architectures. A JWT compactly encodes identity claims, permissions, and metadata into a three-part Base64URL string separated by dots: header.payload.signature.

ScanSuite's free online JWT debugger provides instant decoding and inspection of JWT tokens directly in your browser. Whether you are debugging OAuth 2.0 access tokens from Auth0, Okta, or AWS Cognito, inspecting session tokens in a React application, or validating API gateway bearer tokens, this tool decodes header and payload sections into formatted JSON with syntax highlighting and one-click copy functionality.

ScanSuite's free online JWT debugger instantly decodes JSON Web Tokens into formatted header and payload JSON with syntax highlighting, claim inspection, and editable re-encoding for development testing. All processing runs client-side in your browser, keeping sensitive authentication tokens private while you debug OAuth flows, API authorization, and token expiration issues.

Frequently Asked Questions

What is a JWT debugger?: A JWT debugger is a tool that decodes JSON Web Tokens into readable header and payload JSON, allowing developers to inspect authentication claims, expiration timestamps, and token structure during development and troubleshooting.
Is it safe to paste production JWT tokens into an online debugger?: Only use client-side debuggers like ScanSuite that process tokens locally in your browser. Avoid services that send tokens to remote servers, as decoded payloads often contain sensitive user data and credentials.
What are the three parts of a JWT?: A JWT consists of a header (algorithm and token type), a payload (claims and metadata), and a signature (cryptographic proof of integrity). The three Base64URL-encoded segments are separated by dots.
Can a JWT debugger verify token signatures?: A debugger displays the signature segment but full verification requires the signing secret (for HMAC) or public key (for RSA/ECDSA) and should always be performed server-side in production applications.
What is the difference between decoding and validating a JWT?: Decoding reveals the header and payload contents by reversing Base64URL encoding. Validating additionally verifies the cryptographic signature, checks expiration, and confirms issuer and audience claims match expected values.
What does the exp claim mean in a JWT?: The exp (expiration time) claim is a NumericDate timestamp indicating when the token becomes invalid. Validators must reject tokens where the current time exceeds the exp value.