Postman Sandbox and System Time Zone Interoperability

Confirmed facts

Postman’s pre‑request and test scripts run in a Node.js‑based sandbox. The JavaScript Date object reflects the time zone of the host process:

• new Date(), toString(), and toLocaleString() return values in the local zone.
• toISOString() and all UTC‑specific methods (getUTC*) always return UTC, independent of the host zone.

When the Desktop agent launches, it inherits the operating system’s time zone unless the TZ environment variable is overridden.

Likely explanation for the Web agent

The Postman Web agent executes the sandbox inside the browser’s JavaScript context. Consequently, Date objects there use the browser’s local time zone (the same zone shown in the browser’s date/time settings). Postman does not force a fixed UTC clock for the Web sandbox; UI timestamps may be displayed in UTC, but script‑generated dates follow the browser zone.

Steps to achieve zone‑independent behavior

1. Prefer UTC‑based formatting for any value that will be compared to an API timestamp (which is typically UTC). Use date.toISOString() or date.getTime() for epoch milliseconds.
2. If you need a localized string for logging, explicitly format it with a library that lets you specify the zone, e.g., moment.utc(date).format() or date.toLocaleString(undefined, {timeZone: 'UTC'}).
3. Avoid relying on new Date().toString() or toLocaleString() for assertions; those will differ between Desktop (OS zone) and Web (browser zone).
4. If you must force a specific zone across both agents, launch the Desktop client with a custom TZ variable (e.g., TZ=UTC Postman) and ensure the browser’s timezone is set to the same zone (or adjust scripts to convert to that zone).

Verification tip

In a test script, log:

console.log('Local:', new Date());
console.log('ISO  :', new Date().toISOString());
console.log('Locale:', new Date().toLocaleString());

Compare the output with your system’s time zone (Desktop) and the browser’s time zone (Web). The ISO string will always match UTC, confirming that UTC‑based methods are safe for cross‑agent consistency.