JSON Studio

JWT Decoder

Security

Decode JSON Web Tokens headers, payload claims, and expiration timestamps safely in your browser.

Processed 100% locally in your browser
Encoded JWT String0 chars

Paste a JWT to Decode Claims

Your token signature is never sent to any server.

Technical Documentation & Reference

Comprehensive Guide to JSON Web Tokens (JWT) & Claims

Understand the RFC 7519 open standard, how digital signatures secure distributed microservices, and why decoding tokens client-side protects credentials.

A JSON Web Token (JWT), defined by RFC 7519, is a compact, URL-safe means of representing claims to be transferred between two parties. In modern cloud applications, OAuth 2.0, OpenID Connect (OIDC), and microservice architectures rely heavily on JWTs for stateless user authentication, session management, and access delegation.

A JWT consists of three parts separated by periods (.):

  • Header: Typically consists of the token type (JWT) and the signing algorithm being used, such as HMAC SHA256 (HS256) or RSA SHA256 (RS256).
  • Payload: Contains the claims—statements about an entity (typically, the user) and additional metadata such as subject (sub), issuer (iss), audience (aud), and expiration (exp).
  • Signature: Created by hashing the encoded header, encoded payload, and a secret key (or private key) using the algorithm specified in the header.

Critical Security Notice: Never Share JWTs with Remote Servers

JWT tokens often contain sensitive authorization claims, user emails, scopes, and internal tenant IDs. Pasting active session tokens into third-party cloud utilities can lead to token theft, session hijacking, or compliance breaches. JSON Studio performs all Base64URL decoding directly in browser memory without sending a single byte across the network.

How to Use This Tool

1

Paste Raw JWT String

Paste your encoded Bearer token (three period-separated Base64URL segments) into the input field or click Load Sample.

2

Instant Decoded Claims Breakdown

The decoder immediately extracts and formats the Header and Payload JSON structures with color-coded syntax.

3

Inspect Standard Claims & Expiration

Review human-readable expiration timestamps, issued-at dates, token age, algorithm verification, and subject identifiers.

4

Copy Decoded Header or Payload

Export formatted JSON claims directly to your clipboard for debugging, API testing, or ticket documentation.

Key Features & Capabilities

100% In-Memory Decoding

Zero network transmission. Token strings are parsed and decoded entirely within your local browser context.

Human-Readable Timestamps

Converts epoch timestamps (exp, nbf, iat) into local date strings with countdown indicators showing active or expired status.

Standard Claim Highlighting

Highlights standard RFC 7519 registered claims (sub, iss, aud, jti) for rapid architectural auditing.

Syntax Formatting & Tree Inspection

Formats complex, nested claim payloads with clean 2-space indentation and bracket matching.

Frequently Asked Questions

Can a JWT be decoded without the secret key?
Yes. The Header and Payload of a standard JWT are simply Base64URL-encoded JSON objects. Anyone who possesses the token can decode and read the claims. The secret key is only required to verify or generate the cryptographic signature.
Is it safe to paste production JWTs into JSON Studio?
Yes. Because JSON Studio operates 100% client-side, your token never leaves your device and is never transmitted to any external server or saved in server logs.
What do the standard claims exp, iat, and sub mean?
In RFC 7519, "exp" (Expiration Time) specifies when the token ceases to be valid; "iat" (Issued At) denotes when the token was created; and "sub" (Subject) identifies the principal (user or service) the token was issued for.
What signing algorithms are common for JWTs?
Common algorithms include symmetric HMAC algorithms (HS256, HS384, HS512) and asymmetric public-key signature algorithms (RS256, ES256, EdDSA).

Privacy & Security Guarantee

All data processing, AST syntax repairs, and cryptographic operations happen 100% locally inside your browser using native JavaScript and WebAssembly. No inputs, keys, or file payloads are ever transmitted to or stored on remote servers.