Tool Introduction
The JWT Token Decoder is a powerful and easy-to-use online tool designed specifically for parsing and analyzing JSON Web Tokens (JWT). Whether you are a developer, security expert, or simply interested in the JWT structure, this tool helps you quickly and accurately view the internal composition of a JWT. It splits the Base64 URL-encoded JWT string into three parts: Header, Payload, and Signature, and further decodes the JSON content within the Header and Payload, intuitively displaying core information such as the algorithm, issuer, issued at time, and expiration time.
This tool requires no software installation; JWT decoding can be completed directly in your browser, greatly improving work efficiency.
What is JWT (JSON Web Token)?
JSON Web Token (JWT) is an open standard (RFC 7519) that defines a compact and self-contained way for securely transmitting information between parties as a JSON object. Due to its small size and self-contained nature, JWT is commonly used in authentication, authorization mechanisms, and information exchange scenarios.
A JWT primarily consists of three parts, separated by dots (.):
- Header: Typically contains two parts: the type of the token (i.e., JWT) and the signing algorithm used (e.g., HMAC SHA256 or RSA).
- Payload: Contains claims. Claims are statements about an entity (typically the user) and additional data. Common claims include
iss (issuer), exp (expiration time), sub (subject), aud (audience), etc.
- Signature: Used to verify the sender's identity and ensure that the message has not been tampered with during transmission.
How to Use
- Enter JWT Token: In the "JWT Token" text box on this page, paste the complete JWT Token string you need to decode. The tool provides a default example, which you can use to try it out first.
- Trigger Decoding Operation: The tool will trigger the decoding operation in real-time or automatically after you paste (depending on platform implementation, usually automatic).
- View Decoding Results: After successful decoding, the results will be presented in a clear list format at the bottom of the page, showing the various components of the JWT and the key information parsed from it.
Input Parameter Requirements:
- The input field only accepts a complete string that conforms to the JWT format.
- JWT Tokens are case-sensitive; please ensure that the Token you paste is accurate.
Output Result Format:
The tool will return the following key information in a list format, making it easy for users to quickly understand the JWT content:
- Algorithm (alg): The signing algorithm declared in the JWT header.
- Issuer (issuer): Typically identifies who issued this JWT.
- Issued At (issuedAt): The JWT's issuance time, usually represented as a Unix timestamp.
- Expiration (expiration): The JWT's expiration time; the token becomes invalid after this time.
- Header: The original JSON header content of the JWT.
- Payload: The original JSON payload content of the JWT.
Frequently Asked Questions
- Q: What input formats are supported?
- A: This tool only supports standard, Base64 URL-encoded JWT Token strings as input. Please ensure that the string you provide is complete in structure and conforms to JWT specifications.
- Q: What is the output format?
- A: The output results are displayed in a list format, detailing each component of the JWT (e.g., JSON content of header and payload) and key information parsed from them (e.g., algorithm, issued at time).
- Q: Can I decode a JWT with a tampered signature?
- A: Yes. This tool primarily focuses on decoding the header and payload parts of a JWT and does not verify whether its signature is valid or has been tampered with. Even if a JWT's signature is tampered with, as long as the Base64 URL-encoded format of the header and payload parts is correct, the tool can decode and display its content. However, please note that an invalid signature usually renders a JWT illegal or untrustworthy.
- Q: Why are some fields (e.g., "Issuer" or "Expiration") displayed as empty?
- A: The payload part of a JWT is customizable and is not strictly required to contain all standard fields. If the original JWT Token does not include claims like
iss (issuer) or exp (expiration time), then the corresponding fields in the decoding result will appear empty.
Important Notes
- Data Integrity: Please ensure that the JWT Token you enter is complete and untruncated; any missing or extra characters may lead to decoding failure.
- Privacy and Security: JWT Tokens may contain sensitive information. Although this tool operates client-side, it is still recommended that you avoid pasting JWT Tokens containing highly sensitive information into any untrusted online tools.
- Signature Verification: The primary function of this tool is to parse the content of a JWT; it does not provide signature verification. In practical applications, you should programmatically verify the JWT's signature on the server-side to ensure its authenticity and integrity.
- Timestamp: Issued At (iat) and Expiration (exp) times are usually represented as Unix timestamps (Epoch time). The tool will attempt to convert them to a readable date format, but the actual display may be affected by browser or system time zones.
