Are my private tokens transmitted over the internet?

No! All header decoding runs 100% locally in your browser.

Encoding & Decoding

JWT Header Inspector

Inspect JWT header signing algorithms (HS256, RS256, ES256).

Safe Client-Side Security Suite

API & Secret Key Generator

KEY PREFIX

HEX RANDOM LENGTH (32 chars)

GENERATED HIGH-ENTROPY API KEY

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About JWT Header Inspector

The JWT Header & Algorithm Inspector decodes and analyzes the JOSE header of JSON Web Tokens, identifying signing algorithms (`alg`: RS256, HS256, ES256, EdDSA), Key ID (`kid`), token type (`typ`), certificate chains (`x5c`), and JWKS key set references.

Step-by-Step Guide

How to Use JWT Header Inspector

Step 1

Paste any JWT token into the editor.

Step 2

Inspect the decoded JSON header properties.

Step 3

Review algorithm security details and key identifiers.

Step 4

Click "Copy Header JSON".

Industry Scenarios

Practical Use Cases for JWT Header Inspector

JWKS & Key ID (`kid`) Routing Verification

Inspect the `kid` in JWT headers to confirm your backend or API gateway is retrieving the correct public key from the `/.well-known/jwks.json` endpoint.

Preventing Algorithm Confusion Attacks

Verify that tokens use intended asymmetric algorithms (e.g. RS256 / ES256) rather than vulnerable symmetric algorithms or `alg: "none"`.

Sample Data & Transformation

Input & Output Examples

Inspecting RS256 Header

Input Sample:

eyJhbGciOiJSUzI1NiIsInR5cCI6IkpXVCIsImtpZCI6ImtleS0yMDI2LTA5In0...

Processed Result:

Algorithm (alg): "RS256" (RSA with SHA-256) | Type (typ): "JWT" | Key ID (kid): "key-2026-09"

Technical Capabilities

Key Features & Performance

✓Decodes standard JOSE header parameters: `alg`, `typ`, `kid`, `x5c`, `x5t`, `jku`.
✓Flags insecure configurations like `alg: "none"` or weak HMAC implementations.
✓Explains algorithm cryptographic specifications and recommended key lengths.
✓100% Client-Side memory execution.
✓1-Click Copy header JSON.

Technical Glossary

Key Terminology & Definitions

JOSE Header (Javascript Object Signing and Encryption)

The first base64url-encoded segment of a JWT containing cryptographic metadata regarding how the token is signed and serialized.

Key ID (`kid`)

A unique identifier hint indicating which specific key among a set of keys in a JWKS was used to secure the token.

Frequently Asked Questions (PAA)

JWT Header Inspector FAQs

Asymmetric algorithms like `ES256` (ECDSA P-256) and `RS256` (RSA 2048+) are recommended for distributed systems because authorization servers can sign with private keys while resource servers verify with public keys.