JSON Web Tokens Deep Dive: Decoding Headers, Payloads, Claims & Security Signatures
Published 2026-08-06 | Author: Sarah Connor | Category: dev-experience
Learn the architectural structure of JWTs, OAuth 2.0 stateless authentication, claims verification, and signature hashing.
## Understanding Stateless Authentication with JWTs JSON Web Tokens (JWT), defined under **RFC 7519**, are an open standard for securely transmitting information between parties as a compact, self-contained JSON object. --- ## 1. The 3 Standard Parts of a JWT A JWT string consists of three base64url-encoded parts separated by periods (`.`): ``` eyJhbGciOiJIUzI1NiJ9.eyJzdWIiOiIxMjM0NTY3ODkwIn0.s3cr3t_s1gn4tur3 └───── Header ─────┘ └───── Payload ──────┘ └──── Signature ────┘ ``` 1. **Header**: Specifies signing algorithm (e.g., `HS256` or `RS256`) and token type. 2. **Payload**: Contains JWT claims (e.g., `sub`, `exp`, `iat`, user roles). 3. **Signature**: Verifies that the sender is authentic and message content was not tampered with. --- ## 2. Inspecting Tokens Safely Client-Side Using our **JWT Decoder & Inspector**, developers can inspect token expiry dates and payload claims safely without transmitting session keys to server endpoints.Recommended Developer Tools
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