JWT 解码器
解码并检查 JSON Web Token
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Privacy & Trust
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解码并检查 JSON Web Token
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为什么使用此工具
100% 免费
核心工具可免费使用；AI 及云端工具可能设有每日用量限制。
无需安装
完全在浏览器中运行。无需下载或安装任何软件。
隐私且安全
本地工具把输入留在设备；需要传送数据的工具会清楚标示。
支持移动设备
完全响应式设计——在手机、平板或桌面电脑上均可使用。
Understanding JSON Web Tokens (JWT) Structure and Security
Key Takeaways
- JWTs consist of three Base64url-encoded parts: header, payload, and signature — the payload is readable by anyone, not encrypted.
- Never store sensitive data in JWT payloads — they can be decoded without the secret key. JWTs provide integrity, not confidentiality.
- All JWT decoding happens in your browser — your tokens are never sent to any external server.
JSON Web Tokens (JWT) are the de facto standard for stateless authentication in modern web applications. They carry claims about a user between services without requiring server-side session storage. Understanding JWT structure is essential for debugging authentication flows, verifying token contents, and identifying security issues.
80%+
Of modern web APIs authenticate with JWT
Key Concepts
Three-Part Structure
A JWT has three Base64url-encoded sections separated by dots: the header (algorithm and type), the payload (claims like user ID, expiration), and the signature (cryptographic proof of integrity).
Registered Claims
Standard claims include iss (issuer), sub (subject), aud (audience), exp (expiration), nbf (not before), iat (issued at), and jti (JWT ID). These provide interoperable token metadata.
Signature Algorithms
HS256 uses a shared secret (symmetric), while RS256 uses RSA key pairs (asymmetric). RS256 is preferred for distributed systems where the verifier should not have the signing key.
Security Considerations
Common JWT vulnerabilities include: accepting 'none' algorithm, using weak secrets, not validating expiration, and confusing HS256/RS256 algorithms. Always validate all claims on the server.
Pro Tips
Always check the 'exp' claim — expired tokens should be rejected. Set short expiration times (15–60 minutes) for access tokens.
Use the 'aud' claim to ensure tokens are only accepted by intended services — this prevents token misuse across services.
Store JWTs in httpOnly cookies rather than localStorage to protect against XSS attacks.
Implement token refresh flows with longer-lived refresh tokens stored securely, rather than issuing long-lived access tokens.
All JWT decoding is performed entirely in your browser. Your tokens, which may contain user identity information and authentication claims, are never transmitted to any server. Note: this tool decodes tokens but does not verify signatures.