jwt.verify() returns numeric payload claims as strings

[The-FirstMoon]

Explanation:
I hope you doing great guys
When I use "verify()" in Typescript it is going to return string for everything even the one was a number in the "sign()" object payload.

Summary of the issue:
When signing a JWT with a numeric id claim, jwt.verify() appears to return the claim as a string instead of a number.

A small copy of my code:
const token = jwt.sign(
{ id: 67 },
secret
);
const decoded = jwt.verify(token, secret) as { id: number };
console.log(typeof decoded.id);
Expected behavior:
number
Actual behavior:
string

I checked the value before calling "jwt.sign()" and was confirmed to be a number .

Environment
Node.js: v20.20.2
Package: [jsonwebtoken, @types/jsonwebtoken]
Package version: [^9.0.3, ^9.0.10]
OS: window 11

I hope you have a great day.

[official-burak]

jwt.verify() does not stringify numeric claims. The payload is JSON.stringify on sign and JSON.parse on verify, so a JSON number stays a number.

I ran this on jsonwebtoken@9.0.3 (same major as yours):

const jwt = require('jsonwebtoken');
const decoded = jwt.verify(jwt.sign({ id: 67 }, 's'), 's');
console.log(typeof decoded.id, decoded.id); // number 67

The payload segment is {"id":67,...} with an unquoted number. @types/jsonwebtoken's JwtPayload also does not declare id, so as { id: number } is only a type assertion. It cannot turn a runtime number into a string.

If you are actually seeing a string, id was almost certainly already a string before sign. Typical sources: HTML form fields, query params, process.env, Mongo ObjectId via .toString(), or spreading a parsed JSON body that quoted the value. Log typeof payload.id immediately before jwt.sign.

Do not confuse id with registered string claims. sub / jti are strings by spec. iat / exp / nbf are numbers.

If you paste the compact token (or just the middle payload segment, decoded) we can tell which of those it is.