How to use: JWT Signer
JWT Signer is a free online Security Tools tool that seal a payload with RS256 (or HS256/HS384/HS512 and ES256) right in the browser: paste claims and a PKCS#8 private key — or generate an RSA/EC pair on the spot — then verify the result on the same page. "none" is never accepted, and your keys never leave this machine instantly in your browser. Paste your data, adjust the options and get the result in real time — no installation, no sign-up, and nothing is ever uploaded to a server.
Description
Seal a payload with RS256 (or HS256/HS384/HS512 and ES256) right in the browser: paste claims and a PKCS#8 private key — or generate an RSA/EC pair on the spot — then verify the result on the same page. "none" is never accepted, and your keys never leave this machine.
- Security Tools
- Because everything is computed client-side, JWT Signer is safe to use with sensitive data such as API keys, tokens or private logs.
How to use
Using JWT Signer takes three steps:
- Paste your data into the input box (or load the example).
- Configure the options to match your target format or scenario.
- Copy, download or inspect the output — it updates live as you type.
Run
Examples
Same builder, seeded for signing flows; the live page pre-selects RS256 and activates as soon as you paste a PKCS#8 private key — or generate an RSA/EC pair right on the page (SPKI public export included). Tokens made here verify on this same page.
Output (generated live by the tool just now)
Signed with HS256 — the token below is the compact serialization:
eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJ1aWQiOjQyLCJyb2xlIjoiZGVtbyJ9.j3xOY9SeZp9EnaVLrgVmaRQxSi5ppfol0ImzkJUsr4g
Header: {"alg":"HS256","typ":"JWT"}
Payload: {"uid":42,"role":"demo"}
Paste the token into the Verify mode on this same page (or the JWT Verifier page) to check it; to inspect claims without verifying use the JWT Decoder page. Everything ran in your browser — the secret and key never left this machine.
This output was produced by actually running the tool, not written by hand.
Use cases
Common situations where JWT Signer helps:
- Seal a payload with RS256 (or HS256/HS384/HS512 and ES256) right in the browser: paste claims and a PKCS#8 private key — or generate an RSA/EC pair on the spot — then verify the result on the same page. "none" is never accepted, and your keys never leave this machine.
Parameters
This tool has no options — it works on the input alone.
FAQ
What is JWT Signer?
JWT Signer seal a payload with RS256 (or HS256/HS384/HS512 and ES256) right in the browser: paste claims and a PKCS#8 private key — or generate an RSA/EC pair on the spot — then verify the result on the same page. "none" is never accepted, and your keys never leave this machine. It runs entirely in your browser, so your data stays private.
Is JWT Signer free to use?
Yes. JWT Signer is free, unlimited and works without registration or installation.
Does my data get uploaded?
No. All processing happens locally in your browser; nothing is sent to any server.
Good to know
- Everything runs client-side, so extremely large inputs are limited by your browser tab’s memory rather than by a server upload limit.