What Is Uptime Monitoring? A Developer's Complete Guide

What is uptime monitoring?

Uptime monitoring is the practice of automatically checking whether your website, API, or server is reachable and responding correctly — and alerting you immediately when it isn't.

Without monitoring, you find out about outages when customers complain. With monitoring, you find out before they do. The gap between those two scenarios is your mean time to detect (MTTD), and it directly determines how long outages last and how much they cost.

How it works

A monitoring service sends requests to your endpoints on a set schedule — every 10 seconds, 30 seconds, or 5 minutes depending on your plan. If a request fails, times out, or returns an unexpected response, an incident is created and alerts are dispatched to your configured channels.

Most monitoring tools run checks from multiple geographic regions to distinguish a real outage from a localized network issue. Sentro checks from multiple locations and requires failures to confirm from the primary region before creating an incident.

Monitor types

• HTTP monitors — Check that a URL returns a successful response (2xx status code). Can also validate response headers and body content.
• Keyword monitors — Check that the response body contains (or doesn't contain) specific text. Catches maintenance pages and error states that return 200 OK.
• SSL monitors — Alert you before your TLS certificate expires. Runs daily.
• Domain expiry monitors — Alert you before your domain registration expires.
• TCP monitors — Check that a port is open and accepting connections. Useful for databases, mail servers, game servers.
• Ping monitors — Check basic ICMP network reachability.
• DNS monitors — Verify that your DNS records (A, AAAA, CNAME, MX, TXT) are resolving correctly.
• Heartbeat monitors — Verify that cron jobs and background workers are running by waiting for them to ping a unique URL.

What to monitor first

Start with your most critical user-facing endpoints. The priority order for most SaaS products:

1. Homepage / marketing site (your first impression)
2. Login endpoint (customers can't use your product if this is down)
3. Primary API health endpoint
4. Checkout or payment flow
5. Background jobs (via heartbeat monitors)
6. Third-party dependency endpoints you depend on

Choosing your check interval

Shorter intervals mean faster detection but cost more (or require a higher plan). The right choice depends on the criticality of each endpoint:

Interval	Max MTTD	Best for
10 seconds	~15 sec	Revenue-critical APIs, payment endpoints
30 seconds	~45 sec	Primary application endpoints
1 minute	~90 sec	Secondary endpoints, staging environments
5 minutes	~8 min	Informational, low-criticality, free plan

Alert channels: routing to the right people

The best monitoring setup routes alerts to wherever your team responds fastest. For small teams, Slack is usually the answer. For on-call engineering teams, PagerDuty or OpsGenie integration ensures the right person gets paged and the alert doesn't get lost in a busy channel.

Sentro supports Email, Slack, Discord, Teams, Telegram, Google Chat, Mattermost, PagerDuty, OpsGenie, and custom webhooks — starting at $4/mo. You can mix and match: Slack for immediate awareness, PagerDuty for escalation, email for stakeholders.

The 5-minute setup

1. Create a free Sentro account
2. Click New Monitor, paste your URL
3. Set your check interval (5 minutes on free, 1 min on Starter)
4. Add an alert channel (email or Slack)
5. Create an alert rule: trigger on DOWN, notify via your channel

That's it. Your endpoint is now monitored 24/7. The whole setup takes under 5 minutes, and you'll never be the last person to know about an outage again.