Synthetic Monitoring
Synthetic Monitoring.The lab beside the field.
Scheduled Lighthouse audits on a simulated device, plus lightweight TTFB checks, under ideal and reproducible conditions, right next to the field data from your real visitors. Catch regressions before they ship.
What is Synthetic Monitoring?
A controlled run, on a schedule.
Synthetic Monitoring runs your page through a test lab on a fixed schedule: a simulated device, one location, ideal conditions, fully reproducible. Because the conditions never change, a synthetic run is the clean signal that tells you a regression shipped, before your real users feel it.
It is the counterpart to Real User Monitoring, not a replacement. RUM is the truth from the field, noisy but real. Synthetic is the controlled baseline, reproducible but blind to real conditions. fastmon runs both from the same setup, so you read the lab and reality side by side. Synthetic Monitoring is currently in beta.
Two test typesBeta
Lighthouse and TTFB, on a schedule.
Every monitored page runs two kinds of test, automatically.
Lighthouse · every 24 h
Full Lighthouse audit
- One full run every 24 hours, desktop and mobile in a single pass
- Four categories: Performance, Accessibility, Best Practices, SEO
- Lab metrics: LCP, FCP, CLS, TBT, Speed Index, TTFB
- Cache bypass is on by default, so you measure the uncached worst case
TTFB · every 5 min
Lightweight server check
- A server-response check about every 5 minutes
- Split into DNS, TCP, SSL, server and transfer phases
- Catches backend slowdowns between full audits
- Runs on the same schedule, no extra setup
The audit
Four categories, one run.
Each Lighthouse audit scores your page on the same four categories Google uses, on both desktop and mobile.
Performance
The lab metrics behind the score: LCP, FCP, CLS, TBT and Speed Index on a controlled device.
Accessibility
Automated checks for contrast, labels, roles and the structure assistive tech relies on.
Best Practices
Modern-web checks: HTTPS, correct image sizing, console errors and safe defaults.
SEO
The technical basics search engines expect: meta tags, crawlability and valid markup.
Plans
How many pages you can watch.
Manual pages you add yourself, plus auto pages picked from your top RUM traffic. One-shot ad-hoc tests are always unlimited.
| Plan | Manual pages | Auto pages |
|---|---|---|
| Beta | 5 | 5 |
| Light | 2 | 3 |
| Standard | 5 | 10 |
| Enterprise | 25 | 50 |
One-shot tests run on demand without a schedule and are deliberately unlimited. Limits during the beta; plan mapping may still change.
Lab and field
Two views, one truth.
Neither view is the whole picture. The lab is reproducible but blind to real conditions; the field is real but noisy. fastmon shows both, so a regression in the lab and its impact in the field line up.
Lab · Synthetic
- Simulated device, one location, ideal conditions
- Reproducible, perfect for catching regressions
- Runs on a schedule, before and after a deploy
Field · RUM
- All real visitors, real networks, real devices
- Aggregated at the p75, the truth about the experience
- Includes INP, which the lab cannot measure
FAQ
Synthetic Monitoring, answered.
The questions before you schedule your first test.
How often does a test run?
A full Lighthouse audit runs once every 24 hours, measuring desktop and mobile in a single pass. A lighter TTFB check runs about every 5 minutes to catch backend slowdowns in between. You can also fire a one-shot test on demand.
How does it differ from Real User Monitoring?
Synthetic is a controlled lab test on a simulated device under ideal conditions, reproducible and great for catching regressions. RUM measures your real visitors in the field at the p75. They complement each other, and fastmon runs both. Note that INP is a field-only metric, so it comes from RUM, not the lab.
Which Lighthouse categories are measured?
All four: Performance, Accessibility, Best Practices and SEO, on both desktop and mobile in the same run. Cache bypass is on by default so you always measure the uncached worst case.
How many pages can I monitor?
It depends on your plan. Light watches 2 manual plus 3 auto pages, Standard 5 plus 10, up to Enterprise at 25 plus 50. Auto pages are picked from your top RUM traffic. One-shot ad-hoc tests are always unlimited.
Catch regressions
before they ship.
Scheduled Lighthouse audits, read-only by default: no cookies*, no long-lived identifiers. Hosted in Germany.
Light
€29/month
200,000 pageviews included.
Need debugging and all features? Standard from €99 for 1M pageviews. Enterprise on request. See all plans