Quick Answer: Uptime monitoring checks whether your server responds with an expected status code. Synthetic monitoring runs scripted workflows that mimic real user actions and verifies the application actually works. Start with uptime checks on every critical endpoint. Add synthetic monitoring for revenue paths like login, checkout, and onboarding where a 200 OK can still hide a broken experience.
What is uptime monitoring?
Uptime monitoring answers one question: is the service reachable?
A monitoring probe sends an HTTP request, opens a TCP port, validates a TLS certificate, or resolves a DNS record. If the response matches your expectations (usually a 200 status code within a timeout window), the check passes. If not, you get alerted.
This is the foundation of production monitoring. It catches server crashes, load balancer misconfigurations, expired certificates, DNS failures, and network outages. It is fast, cheap, and runs every 30 to 60 seconds without heavy infrastructure.
What uptime monitoring does not catch: a page that returns 200 but renders a blank screen because JavaScript failed to load. An API that responds OK but returns an error payload. A checkout flow where the payment button stopped working after a deploy. A login form that submits but never redirects.
Your server can be "up" while your application is broken. That gap is why synthetic monitoring exists.
What is synthetic monitoring?
Synthetic monitoring (sometimes called transaction monitoring or browser monitoring) simulates real user behavior on a schedule.
Instead of pinging a URL, a synthetic check might:
- Load your homepage in a headless browser
- Click "Sign In" and fill in test credentials
- Verify the dashboard loads with the expected heading
- Measure how long each step took
Synthetic checks use tools like Playwright or Puppeteer to execute multi-step workflows. They catch problems uptime checks miss: JavaScript errors, broken CSS, failed third-party scripts (Stripe, Google Maps, analytics), form validation bugs, and redirect loops.
The tradeoff is cost and complexity. A synthetic check takes 5 to 30 seconds and uses more resources than a simple HTTP ping. You run them less frequently (every 1 to 5 minutes) and on fewer paths. You also maintain test scripts that break when your UI changes.
When should I use uptime monitoring vs synthetic monitoring?
Think of them as two layers, not a choice between one or the other.
Use uptime monitoring for:
- Homepage and marketing site availability
- API health endpoints and critical REST routes
- Database connection proxies and internal services
- TLS certificate expiry and DNS resolution
- TCP port checks on mail servers, Redis, or message queues
- Background job heartbeats (did the cron actually run?)
Use synthetic monitoring for:
- Login and authentication flows
- Checkout and payment completion
- Multi-step onboarding wizards
- Search functionality that depends on JavaScript
- Pages with heavy client-side rendering
- Third-party integration verification (payment gateway, SSO provider)
A practical starting point for a SaaS app:
| Layer | What to monitor | Tool type |
|---|---|---|
| Infrastructure | API health endpoint, homepage, TLS cert | Uptime |
| Authentication | Login with test account, session persistence | Synthetic |
| Core workflow | Create resource, view dashboard, delete resource | Synthetic |
| Background jobs | Nightly export, invoice generation | Heartbeat/uptime |
If you are a solo developer or early-stage startup, get uptime monitoring running on day one. Add one synthetic check for your most critical user flow when you have paying customers depending on it.
How do I combine uptime and synthetic monitoring without alert fatigue?
The biggest mistake teams make is treating every monitor equally. A homepage uptime failure and a slow checkout synthetic check should not page the same person at the same urgency.
Tier your monitors by business impact:
- Page immediately: Production API down, payment flow broken, auth unavailable
- Notify in Slack: Degraded response times, non-critical endpoint failures
- Log and review: Staging environment issues, certificate expiring in 30 days
Use uptime monitoring for broad coverage. Put an HTTP check on every service that can fail independently. Validate response bodies where it matters: check that your health endpoint returns {"status":"ok"}, not just a 200. Monitor TLS and DNS so preventable certificate and resolution failures never become outages.
Use synthetic monitoring for depth on critical paths. One well-maintained synthetic check on your login flow is worth more than ten shallow homepage pings. Keep the scripts short, use stable selectors (data-testid attributes, not CSS classes that change every sprint), and run them from at least two geographic regions.
Bridge the gap with degraded alerts. A site that responds in 8 seconds is technically "up" but functionally broken for users. Good uptime tools flag degraded performance when latency exceeds a baseline, giving you a warning before the timeout triggers a hard down alert. This catches slowdowns that neither a binary up/down check nor a full synthetic suite might surface immediately.
Overwatch covers the uptime layer with HTTP, TCP, TLS, DNS, and heartbeat checks, plus configurable latency thresholds that mark endpoints as degraded before they go fully down. Pair that with synthetic tools for your critical user journeys and you have coverage from infrastructure to experience.
What does a minimal monitoring stack look like?
Here is a setup most teams can deploy in an afternoon:
Step 1: Uptime checks (15 minutes). Monitor your homepage, API health endpoint, and any service your app depends on (auth provider status page does not replace checking your own auth route). Set 60-second intervals and 2 to 3 consecutive failure thresholds.
Step 2: Dependency checks (10 minutes). Add TLS expiry monitoring (alert at 30 and 7 days). Add DNS resolution checks for your primary domain. These prevent the most embarrassing outages: the ones where your cert expired and nobody noticed.
Step 3: Alert routing (10 minutes). Send critical failures to Slack or PagerDuty. Send warnings to a lower-priority channel. Test every channel before you rely on it.
Step 4: One synthetic check (30 to 60 minutes). Pick your highest-value user flow. Write a Playwright script that completes it end to end. Run it every 5 minutes from two regions. This is your safety net for "the server is up but the app is broken."
Step 5: Review monthly. Track which alerts were real incidents vs false positives. Retire monitors for deprecated endpoints. Update synthetic scripts after UI changes.
For background jobs and scheduled tasks, uptime checks on your homepage will not help. Use heartbeat monitoring so each job pings on success and you alert when the ping goes missing. (We covered that workflow in How to Monitor Cron Jobs with Heartbeat Monitoring.)
Frequently Asked Questions
What is the difference between uptime monitoring and synthetic monitoring?
Uptime monitoring sends a simple HTTP or TCP request and checks whether the server responds with an expected status code. Synthetic monitoring runs scripted browser or API workflows that mimic real user actions, like logging in or completing checkout. Uptime catches server and network failures. Synthetic catches broken JavaScript, failed form submissions, and third-party integration outages.
Do I need synthetic monitoring if I already have uptime monitoring?
If your application has multi-step user flows that generate revenue or handle authentication, yes. Uptime monitoring can show green while your checkout button is broken or your login form returns a JavaScript error. Synthetic monitoring is the second line of defense for anything where a 200 OK is not enough proof the app works.
Is synthetic monitoring the same as real user monitoring (RUM)?
No. Synthetic monitoring runs automated tests on a fixed schedule from known locations. RUM collects performance data from actual visitors in their real browsers and networks. Synthetic gives you a consistent baseline and catches regressions before users hit them. RUM shows what real users experience, including device and geography variance.
How often should I run synthetic checks?
Every 1 to 5 minutes for critical flows like login and checkout. Synthetic checks are heavier than uptime pings because they may launch a headless browser and execute multiple steps. Running them every 30 seconds is usually unnecessary and expensive. Match frequency to business impact: payment flows deserve tighter intervals than a marketing blog.
Can I start with uptime monitoring only?
Yes, and most teams should. Uptime monitoring is cheaper, faster to set up, and catches the majority of outages: server crashes, DNS failures, TLS expiry, and network partitions. Add synthetic monitoring once you have baseline uptime coverage on your API, homepage, and infrastructure dependencies, and you have user flows where a passing HTTP check is not enough.
Uptime monitoring is your first line of defense. Synthetic monitoring is your second. Overwatch handles the uptime layer with HTTP, TCP, TLS, DNS, and heartbeat checks, degraded latency alerts, and notifications to Slack, Discord, Teams, email, or any webhook. Get your infrastructure covered today, then layer synthetic checks on your critical user flows. Get started free →