Input

ISO-8601 Builder

Toggle formatting rules to generate strict API-ready ISO-8601 and RFC-3339 compatible strings.

Base Date-Time

Include MillisecondsInclude Timezone OffsetUse UTC (Z)Date Only

Output

Live Preview

Valid ISO-8601

2026-04-27T13:04:53.000Z

Language Snippets

JavaScript

new Date().toISOString();

Python

from datetime import datetime, timezone

datetime.now(timezone.utc).isoformat()

C#

DateTimeOffset.UtcNow.ToString("O");

What is this tool and how do you use it?

ISO-8601 / RFC-3339 Formatter is designed for API engineers who need strict, predictable datetime strings across services, queues, and databases. Timestamp bugs often happen when one system expects UTC with a trailing Z, another expects offsets, and a third strips milliseconds. This builder makes those choices explicit. You can toggle milliseconds, timezone offset, UTC mode, and date-only output, then inspect a live preview that updates instantly. A validation indicator checks whether the result matches ISO-8601 structure so you can catch format mistakes before requests fail in production. To use the tool, choose a base datetime, switch the toggles to the target contract required by your API, and copy either the preview value or a language snippet for JavaScript, Python, or C#. This workflow is ideal for payload contracts, SDK examples, ETL mapping, and OpenAPI documentation where timestamp consistency is critical for consumers and downstream systems.

If you receive raw epoch numbers, convert them first in Smart Epoch Converter. To coordinate deployment cutovers across teams, use Global Meeting Slicer. For operational log cleanup after release, continue with Log Timestamp Normalizer.