User Agent Generator: Build and Test UA Strings for Any Browser

Every HTTP request your browser sends carries a small piece of identification called the User Agent (UA) string. Servers read it to decide which version of a page to serve, analytics platforms count on it, and testing tools depend on it to simulate different devices. Yet hand-writing a valid UA string is surprisingly error-prone — one missing parenthesis or wrong token order and your test no longer represents a real browser.

That is exactly the problem the User Agent Generator solves. It gives you a library of ready-to-use UA strings for Chrome, Firefox, Safari, Edge, mobile browsers, and even Googlebot, plus a custom builder that combines any browser, operating system, and device type into a syntactically correct string. Everything runs 100% client-side, so no UA string or request data ever leaves your browser.

Whether you are a QA engineer building a cross-browser test matrix, a developer debugging device detection logic, or an SEO specialist verifying how crawlers see your site, this guide will show you how to get the most out of the tool.

Why Use a User Agent Generator?

• Accuracy by construction. Real UA strings follow strict formatting conventions. The generator produces strings with the correct token order, version separators, and platform notation, so the output behaves like a genuine browser header rather than a plausible-looking fake.
• Save time during testing. Instead of hunting through browser documentation or copying from old Stack Overflow answers, you get a curated library of current UA strings for every major browser and operating system combination in one click.
• Simulate the full device spectrum. Test desktop (Windows, macOS, Linux), mobile (iOS, Android), and crawler traffic (Googlebot, curl) without physically owning each device or spinning up emulators.
• Zero privacy risk. The tool is entirely client-side. Nothing is uploaded, logged, or transmitted — important when you are working with internal URLs or pre-release products.
• Free with no signup. No account, no API key, no rate limit. Open the page, copy a string, and get back to work.
• Reliable copy-paste output. The output box strips formatting artifacts and gives you a clean string that pastes directly into curl -A, Postman headers, Playwright configs, or custom HTTP clients.

Key Features

The custom builder is the standout feature: pick any of the four browsers (Chrome, Firefox, Safari, Edge), any of the five operating systems (Windows, macOS, Linux, iOS, Android), and desktop or mobile, and the tool assembles the correct platform token and engine notation for that combination — including edge cases like Chrome-on-iOS, which uses the CriOS token instead of Chrome.

The "use current browser" button is a quiet time-saver. When you need your own UA string — for setting up analytics filters or whitelisting test traffic — one click captures it exactly, with no risk of a transcription typo.

How to Use

1. Open the User Agent Generator — the output box is preloaded with a Chrome-on-Windows string so you can see the format immediately.
2. Browse the preset library and click Select on any UA string you want to work with, or click Random to grab an arbitrary one.
3. Need something specific? Scroll to the custom builder, choose your browser, OS, and device type, then click Use to load the generated string into the output box.
4. Click Copy to send the string to your clipboard — you will see a confirmation when it succeeds.
5. Paste the string wherever you need it: a User-Agent request header, a test configuration file, or a bot-detection rule set.

Understanding User Agent Strings

A modern Chrome UA string looks like this:

Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/124.0.0.0 Safari/537.36

It looks chaotic, but every segment has a meaning and a history:

1. Mozilla/5.0 — the compatibility token. Almost every browser claims to be Mozilla for historical reasons: in the 1990s, servers checked for "Mozilla" before sending modern features, so browsers adopted the token and never dropped it. Today it carries almost no information — every major browser sends it.
2. (Windows NT 10.0; Win64; x64) — the platform token. This is where the operating system and architecture live. macOS reports Macintosh; Intel Mac OS X 10_15_7, desktop Linux uses X11; Linux x86_64, and Android devices report Linux; Android 14; Pixel 8 with the model name included.
3. AppleWebKit/537.36 (KHTML, like Gecko) — the layout engine. Chrome, Edge, and Safari all descend from WebKit and keep this token for compatibility. Firefox instead reports its Gecko engine as Gecko/20100101. This segment is the most reliable way to distinguish engine families.
4. Chrome/124.0.0.0 — the real browser token. This is the part parsers actually trust. Edge appends Edg/124.0.0.0 after the Chrome token (Edge is Chromium-based), Safari reports Version/17.4 Safari/605.1.15, and Chrome on iOS uses CriOS/124.0.0.0 because Apple requires all iOS browsers to use WebKit.

You may have heard that UA strings are being replaced by User Agent Client Hints. That is true — Chromium browsers now serve a "reduced" UA string and expose detailed information through Sec-CH-UA response and request headers. But classic UA strings are nowhere near dead: they remain the primary identifier in server logs, CDN rules, analytics pipelines, and third-party clients like curl and scrapers. For testing and interoperability work, understanding and generating full UA strings is still an essential skill — and likely will be for years.

Practical Use Cases

Testing responsive and conditional serving

Many sites serve different HTML, redirects, or feature flags based on the User Agent. Before shipping a mobile-only redirect or a browser-specific workaround, replay the request with the exact UA strings for iPhone Safari, Android Chrome, and desktop Firefox to confirm each branch of your detection logic behaves as intended. The generator gives you all three in under a minute.

Web scraping and API clients

When you build a scraper or API client, the default UA string of your HTTP library (often python-requests/2.x or Go-http-client) is immediately recognizable and frequently blocked. Setting a realistic browser UA string is standard practice for legitimate scraping of pages whose terms allow it. Pair it with the cURL to Code Converter to turn a tested request into ready-to-run code in your language of choice.

SEO and crawler verification

If you serve special content to search engines or want to verify that your bot-detection rules treat Googlebot correctly, you need the real Googlebot UA string: Mozilla/5.0 (compatible; Googlebot/2.1; +http://www.google.com/bot.html). It is in the preset library, ready to copy. Use it to confirm your robots.txt rules, log filters, and CDN bot modes behave correctly — and remember that genuine Googlebot verification also requires a reverse DNS check, not just the UA string alone.

QA cross-browser matrices

Building a test matrix across 4 browsers × 5 operating systems × 2 device types is 40 combinations. The custom builder lets you enumerate them systematically: fix the browser, sweep the OS list, flip the device toggle, and record the generated strings directly into your Playwright or Selenium configuration. No device farm required for the header-level tests.

Best Practices

• Keep UA strings realistic. A syntactically valid, current-looking UA string tests what you intend to test. A mangled or ancient string may route your traffic into legacy code paths that real users never hit.
• Never spoof for fraud or ToS violations. Pretending to be Googlebot to bypass paywalls, or masking a bot as a human user against a site's terms, can get IPs blocked and accounts banned. Use spoofing for testing systems you own or have permission to test.
• Refresh version numbers periodically. Browsers update every few weeks. If your test fixtures pin Chrome/90, detection libraries may classify the string as suspiciously old. Regenerate presets periodically to stay current.
• Test both desktop and mobile. Mobile UA strings carry extra tokens (Mobile, model names) that some parsers mishandle. Include at least one Android and one iOS string in every detection-logic test suite.
• Verify bot claims properly. If you run a website, do not trust the Googlebot UA string alone — validate crawlers with reverse DNS (.crawl.google.com or .googlebot.com) before allowing special treatment.
• Respect robots.txt when crawling. Sending a browser UA string does not exempt you from crawling rules. Check robots.txt and rate-limit your requests regardless of which UA string you send.

Start Generating User Agent Strings Today

The User Agent Generator removes the most tedious part of browser simulation: producing correct, current UA strings on demand. With a curated preset library, a flexible custom builder, and one-click copy — all running privately in your browser — it fits naturally into any testing, scraping, or SEO workflow.

Open the tool, grab a string, and make your next test run that much more faithful to the real world.

Related Tools You Might Like:

• User Agent Parser — paste any UA string and decode it back into browser, engine, operating system, and device. The perfect companion for verifying that the strings you generate parse the way you expect.
• cURL to Code Converter — turn a tested cURL command (headers included) into ready-to-run code for Python, JavaScript, Go, and more.
• HTTP Headers Viewer — inspect the full set of request and response headers in one place to see exactly how your User-Agent travels alongside the rest.

Happy testing!