What is Online JWT Encoder/Decoder?

The JWT Encoder/Decoder is a powerful, free online tool designed for encoding and decoding JWT (JSON Web Token). JWTs are a popular standard for securely transmitting JSON data by signing it with a unique key. This tool allows you to encode a JWT using a signing key, verify a JWT using a public or private key, and even decode a JWT without verifying the signature. It is an essential tool for anyone working with authentication or secure data transfers.

The tool supports multiple signing algorithms, including HS256, HS384, HS512, RS256, RS384, RS512, ES256, ES384, and ES512. The HS (HMAC) algorithms use a single signing key for both encoding and decoding (symmetric algorithms), while RS (RSA) and ES (Elliptic Curve) algorithms use a pair of keys—a private key for encoding and a public key for decoding (asymmetric algorithms).

JWTs consist of three parts: the header, payload, and signature, separated by dots. This structure looks like “header.payload.signature”. Each part is base64 encoded, and while anyone can view the header and payload after decoding, the signature ensures that the data is tamper-proof.

JWTs also contain predefined claims such as “iss” (issuer), “exp” (expiration time), “sub” (subject), and “aud” (audience). Stored in the payload, these claims help define and validate the token’s data—meanwhile, the header stores metadata like the algorithm used.

With this tool, you can either verify the signing key when decoding a JWT or simply view the content without verification. The payload and header will always be visible, but without the correct key, you cannot validate the signature.

If you use HS (HMAC) algorithms, it is important to use strong signing keys of appropriate lengths (e.g., 32 characters for HS256, 48 characters for HS384, and 64 characters for HS512) to avoid brute-force attacks. Reference: [Importance of Using Strong Keys with JWT]

How to Use Online JWT Encoder/Decoder?

Using the JWT Encoder/Decoder tool is straightforward, and it allows you to encode, decode, or debug a JWT with ease. Follow these steps:

1. Encode a JWT:
   • Fill in the input field with the JSON payload that you wish to encode.
   • Select the algorithm you wish to use for signing and fill in the signing key if needed.
   • Click the “Encode” button. If everything is correctly configured, the tool will output a valid JWT.
2. Decode a JWT:
   • Fill in the input field with the JWT you wish to decode.
   • If you want to verify the JWT, check the “Verify JWT key?” box and fill in the signing key and algorithm details.
   • Click the “Decode” button. If successful, the tool will display the decoded payload and header.
3. Security Analysis:
   • Whenever you encode or decode a JWT, the tool will also run a background security analysis. This analysis checks the strength of your algorithm, key length, and the presence of recommended claims, providing insights into the security of your JWT.

Security Note

All processing, including encoding, decoding, and security analysis, takes place in your browser. This means that none of the JWTs, signing keys, or public/private key pairs are ever transferred to any server, ensuring your data remains private. However, it is strongly advised that you protect your signing keys and key pairs, especially when they are critical to your application’s security. Always avoid using sensitive data in online tools, even when they are client-side.

Key Features of JWT Encoder/Decoder Tool

• Supports 9 Algorithms: HS256, HS384, HS512, RS256, RS384, RS512, ES256, ES384, and ES512.
• Encode and Decode: Easily encode JWTs with custom payloads and signing keys or decode and view JWT details.
• Automatic Security Analysis: Analyze the security of JWTs automatically after encoding or decoding.
• Client-Side Processing: All operations are done in your browser for maximum privacy.
• Predefined Claims: Utilize claims like “iss”, “exp”, “sub”, and more for better definition and validation of tokens.