JWT Size Checker
Check how big a JSON Web Token is in bytes. See the size of the header, payload, and signature, find the largest claims, and test the token against HTTP header limits of nginx, Apache, Node.js, and more.
Input
Output
| Part | In the token | Decoded | Share |
|---|---|---|---|
| Paste a JWT to see its parts | |||
| Claim | Size in the token | Share of payload |
|---|---|---|
| Paste a JWT to see its claims | ||
| Limit | Applies to | Max | Used | Status |
|---|---|---|---|---|
| Paste a JWT to check the limits | ||||
Readme
What this tool does
JWT size checker tells you how big a JSON Web Token is and whether it is likely to fit common server header limits. Paste a raw token or an Authorization: Bearer ... header and it breaks the token into parts, estimates the size of each part, and compares the total against common limits from Apache, nginx, Tomcat, Node.js, and AWS ALB.
Features
- Shows the total token size in bytes, and KiB when the token gets large
- Breaks JWS and JWE tokens into their parts so you can see where the size goes
- Estimates the size of top level claims in signed tokens and flags limits that are close or over
How it works
The tool strips the Bearer prefix and any whitespace before parsing the token. It accepts the usual 3 part signed JWTs and 5 part encrypted JWTs.
For signed tokens, it also reads the payload when it is valid JSON and lists the largest claims first. For encrypted tokens, the payload cannot be inspected, so the size breakdown is limited to the token parts.
When to use it
Use this when a JWT is too large for a request header, when you want to see which part of the token is growing, or when you need a quick check before sending tokens through proxies or load balancers with strict header limits.