Free website monitoring with real-time alerts

Website monitoring: why you need to track URL availability

Website monitoring is the practice of continuously checking the availability, latency, and integrity of an HTTP URL. A monitoring tool sends a request at a regular interval, records the response, and triggers an alert on failure. This lets you catch an outage before your users do.

A 2024 Gartner study puts the average cost of one hour of downtime at $5,600 for a small business and up to $540,000 for a Fortune 1000 company. Without uptime monitoring, you discover the incident through an angry customer email, sometimes hours after the outage. In the meantime, your conversion funnel is broken, your forms no longer submit, and your SEO degrades.

CaptainDNS provides a free tool to monitor up to 5 HTTP URLs. Each endpoint is checked every 5 minutes from our probes hosted in the European Union. On every check, we record the HTTP code, latency in milliseconds, and the content of any critical headers (Cache-Control, X-Robots-Tag). If an abnormal response is detected, you receive an instant email alert.

Typical HTTP monitoring use cases

• Watch a homepage: detect an application crash or a hosting outage before your visitors do.
• Monitor a public API: confirm that a REST endpoint returns a 200 code and a valid payload.
• Track a payment funnel: make sure the checkout page stays reachable 24/7.
• Audit a corporate site: prevent SEO traffic loss caused by prolonged 5xx errors.
• Cover a migration: during a hosting change or a deployment, watch for regressions.
• Protect a landing page: detect downtime within minutes before launching a marketing campaign.

The standard English term is website uptime monitoring or http monitoring. The historical players (UptimeRobot, Pingdom, StatusCake, BetterStack) have offered this service for over 15 years. CaptainDNS brings a European approach, integrated into a broader DNS and email ecosystem.

How the CaptainDNS HTTP monitoring tool works

Our tool runs an HTTP check every 5 minutes on each of your monitors. Here is what happens on every check:

1. DNS resolution

CaptainDNS first resolves the URL hostname through our internal DNS resolvers. DNS latency is measured and recorded separately. If resolution fails (NXDOMAIN, SERVFAIL, timeout), the check is marked as dns_error and an alert is triggered.

2. TCP handshake and TLS negotiation

A TCP connection opens to the resolved IP. For HTTPS URLs, a TLS handshake is negotiated. CaptainDNS validates the certificate chain, the expiration, and the hostname match. An expired or invalid certificate triggers a tls_invalid alert.

3. HTTP request and response read

An HTTP request (GET by default, or the configured method) is sent. CaptainDNS waits for the response for up to 30 seconds. Beyond that, the check is marked as timeout. The HTTP code, headers, and total latency are recorded.

4. Evaluating the check result

By default, CaptainDNS marks a check as up if the HTTP code falls in the 200-399 range. You can customize the expected codes (for example only 200 and 301). A 5xx code, a timeout, or a network error marks the check as down.

5. Storage and alerting

The result is stored in the database for 30 days. If the monitor state flips from up to down, an email alert is sent immediately. When the state returns to up, a recovery email is sent to close the incident.

Multi-zone check regions by plan

Your checks run from several regions depending on your plan: Europe (default, locked on the free plan), United States, and Asia-Pacific. The infrastructure runs on Fly.io, which makes it easy to add regions without rewriting your monitor.

The free plan runs from 1 region (Europe), Pro from 2 regions of your choice, Business and Enterprise from all 3 regions. A multi-region check lets you tell a real global outage apart from a regional network disruption, something a single-region check cannot do. The next section covers how it works and the associated detection strategies.

Monitor your site from multiple regions

A single-region monitor only tells you part of the story. If your only probe lives in Europe and a transit provider between Europe and North America has an issue, you see your site as "up" while your US customers cannot reach it. Conversely, a local network incident near the probe makes you think there is a global outage. Multi-region monitoring solves both cases.

Three regions available

CaptainDNS runs your checks from three geographic zones:

• Europe (eu): covers the EU, United Kingdom, and North Africa, low latency for European audiences
• United States (us): covers North America and part of Latin America
• Asia-Pacific (apac): covers Japan, Korea, Southeast Asia, and Oceania

Probes run on Fly.io. Adding a region to a Pro or Business monitor takes one click, without resetting your history.

Three configurable DOWN detection strategies

Running several probes raises a question: how many regions need to fail before the site is considered DOWN? CaptainDNS lets you pick from three strategies.

• Consensus (default): the monitor flips DOWN when the majority of regions fail. This is the recommended balance for 90% of cases. You avoid false positives caused by a network incident in a single region, while still reacting quickly on a real outage.
• Strict: a single region going DOWN is enough to trigger the alert. Suited for critical monitors (payment, real-time API) where any regional flap must surface, even brief, even localized.
• Unanimous: the monitor only flips DOWN if every region fails. Suited for B2C applications with geographically distributed infrastructure (active-active CDN, edge compute) that tolerate regional flaps without treating them as real user-facing incidents.

Who gets what

Free and Starter are locked to Consensus by design: with a single region, the three strategies produce the same result, so showing a choice that is not really a choice adds no value. Pro and above unlock both multi-region and strategy selection.

See plans and pricing for the full details.

Real-time email alerts when your site goes down

Alerting is the heart of any monitoring tool. CaptainDNS sends an email alert the moment a check fails, with minimal friction and zero spam.

Trigger conditions

Built-in anti-spam

Without precaution, a flapping site (alternating up/down) can generate dozens of alerts per hour. CaptainDNS applies three mechanisms to avoid this:

1. Two-check confirmation: before sending an alert, CaptainDNS runs a second immediate check from a different probe. If both fail, the alert is sent. This eliminates false positives caused by local network incidents.
2. Per-incident grouping: during continuous downtime, only one alert is sent at the start. No interim alerts as long as the site stays down. A recovery alert is sent when the site comes back up.
3. Auto-disable: if a URL stays down for more than 7 consecutive days, CaptainDNS sends a warning email and automatically disables the monitor. You avoid receiving alerts on URLs that are permanently dead.

Alert email format

The email contains the strict minimum needed to understand the incident:

• URL involved
• HTTP code or error type
• Latency of the last successful check
• UTC timestamp and local time
• Direct link to the dashboard to rerun a manual check

No image tracking, no marketing pixel, no third-party tracker links. The email is minimal and functional.

Notifications: email and webhooks

Email covers 90% of alerts. But as soon as you want to route to Slack, Discord, PagerDuty, Opsgenie, or an internal incident management system, email is no longer the right channel. That is why CaptainDNS complements email alerts with a configurable HTTP webhook channel.

Email by default, included everywhere

Every plan, including the free plan, sends unlimited email alerts to the recipient address on your account. Nothing to configure beyond the monitor itself.

Webhooks V2: a customizable HTTP channel

On paid plans, you can register one or more HTTPS endpoints that will receive monitoring events (and events from other categories) as JSON POST requests. These webhooks fit naturally with:

• Slack through an Incoming Webhook
• Discord through a channel webhook
• PagerDuty or Opsgenie through their Events API endpoint
• your own backend (internal bot, on-call, ops dashboard)

Each endpoint is signed with a shared secret so you can validate the origin of the POST on the receiver side.

Notification categories

You are not forced to receive everything on a single channel. CaptainDNS organizes events into categories:

• Monitoring: up / down incidents, recoveries, auto-disable
• Hosting: certificate renewals, DKIM key rotations, MTA-STS and BIMI events
• Security: blacklist detections, DMARC alerts, critical DNS changes
• Digest: weekly and monthly summaries
• System: quota thresholds, plan changes, CaptainDNS incidents

Each webhook can subscribe to one or more categories. You can route monitoring to your Slack ops channel and security to PagerDuty, for instance.

Automatic retries and history

If delivery fails (5xx, timeout, non-2xx), CaptainDNS retries with exponential backoff. Every attempt is logged: HTTP code received, latency, error details. You can review the full history from the dashboard to debug a webhook that stopped receiving.

Webhook quotas by plan

See plans and pricing for the full details.

Uptime metrics, p95 latency, and 30-day heatmap

The dashboard aggregates your checks into clear visual metrics. No cluttered charts, no paywall on the essentials.

Core metrics

The p95 latency is the right indicator of perceived performance. The average hides spikes, while p95 tells you what your users experience in the worst 5% of cases.

30-day heatmap

The heatmap visualizes the last 30 days as a colored grid. Each cell represents a time window (1 hour or 1 day depending on zoom):

• Green: every check in the window succeeded
• Orange: a few checks failed (brief incident or flapping)
• Red: most checks failed (long incident)
• Gray: no data (monitor disabled or not yet created)

A single glance is enough to spot problematic periods and correlate them with an application change. The heatmap is free and unlimited, unlike several competitors who reserve it for paid plans.

Detailed history

Every individual check can be reviewed for 30 days: timestamp, HTTP code, DNS latency, TLS latency, total latency, response headers. You can filter by status (up only, down only, TLS errors) or by date range to debug a specific incident.

Comparison of website monitoring tools

Here is how CaptainDNS positions itself against the main website monitoring tools (UptimeRobot, BetterStack, Pingdom).

Unique CaptainDNS advantages

1. Unified stack: a single login to manage DNS, SPF/DKIM/DMARC, email blacklist monitoring, TLS certificates, and HTTP uptime. Specialized players force you to juggle 4 or 5 tools.
2. Made in EU for storage: database in France, backups in France, team based in Europe. European probes run in France and Germany; United States and Asia-Pacific probes (optional) only execute checks, with no data storage outside the EU.
3. No artificial paywall: the heatmap, p95 latency, and 30-day history are included in the free plan. Most competitors lock these behind $15 or more per month.
4. Smart auto-disable: no other tool offers this mechanism. You avoid noise on permanently dead URLs.
5. Configurable multi-region: up to 3 zones (Europe, United States, Asia-Pacific) with 3 DOWN detection strategies to choose from, starting at the Pro plan. Competitors force a single locked mode.
6. Long history: 30 days on the free plan, up to 730 days on Enterprise. Useful for annual SLA reviews and historical incident correlation.

When another tool still makes sense

UptimeRobot remains unbeatable if you need to monitor more than 50 URLs on a free plan. BetterStack excels at advanced status pages with strong branding. Pingdom is interesting for very large companies already paying for the SolarWinds suite.

CaptainDNS targets developers, freelancers, agencies, and European SMBs that want a simple, free, GDPR-compliant tool integrated into their DNS and email stack.

Quotas, limits, and plans

CaptainDNS practices full transparency on quotas. No fine print, no surprises.

Free plan

• 5 simultaneous HTTP monitors
• 1 check region (Europe, locked)
• Consensus strategy (locked) (single region, no real choice to make)
• Check every 5 minutes (288 checks per day per monitor)
• 1 public status page
• 30 days of detailed history per check
• Unlimited email alerts to a recipient address
• Public API: 500 credits per month
• No credit card required

Quota summary by plan

See plans and pricing for full details (pricing, API credits, add-on options).

Upgrade path: when to change plan

• Need more than 5 monitors or a white-label status page: Starter
• Need to monitor from the United States or Asia-Pacific (2 regions), or pick a detection strategy: Pro
• Need all 3 regions at once and comfortable quotas (250 monitors, 40 status pages, 25 webhooks): Business
• Need at least one year of detailed history, large volumes (2500+ monitors), or contractual support: Enterprise

Cases not covered by CaptainDNS

• Raw TCP monitoring on non-HTTP ports (SMTP, FTP, database)
• Multi-step transactions (user journey across several pages with assertions)
• Probes in regions other than Europe, United States, and Asia-Pacific (for example South America, Africa, Middle East)
• Status pages with a custom domain (status.captaindns.com)

Slack, Discord, PagerDuty, and Opsgenie alerts are covered by webhooks V2 (available starting Starter). You configure an HTTPS endpoint on the CaptainDNS side and let the destination handle final formatting.

Why 5 monitors and not 50 on the free plan?

The free plan must remain financially sustainable. A check every 5 minutes represents around 8,600 HTTP requests per month per monitor. With 5 monitors per free account, the infrastructure cost stays manageable while still covering the real needs of a freelancer or a small team (homepage, API, payment page, blog, customer dashboard).

If your need exceeds 5 monitors, move to Starter or reach out for an extended quota dedicated to open source and nonprofit projects.

European hosting and data sovereignty

HTTP monitoring is a data processing activity: you send URLs, optional headers, and sometimes authentication tokens. GDPR applies as soon as an end user is identifiable or the processing concerns a European service.

EU hosting and processing

CaptainDNS runs its data plane from the European Union:

• European probe in France and Germany (default on every plan)
• PostgreSQL database in France
• Backups in France, with no transfer outside the EU
• Technical team based in Europe

United States and Asia-Pacific probes are optional (Pro plan and above). If you stay on the free or Starter plan, your monitor only runs from Europe and no data crosses the Atlantic. Primary storage of results always stays in France regardless of plan and active regions: only the checks execute remotely, and their results are immediately sent back to the European database.

No tracking cookies

The CaptainDNS dashboard uses no tracking cookies, no marketing pixels, and no third-party analytics scripts. Authentication runs on Auth0 hosted in the EU. The only data recorded is what is strictly required for the service: your email, your monitors, and your check results.

Comparison with competitors based outside the EU

UptimeRobot, Pingdom, BetterStack, and StatusCake host their data in the United States or the United Kingdom. Even when these players offer a DPA addendum, their probes often remain located outside the EU and their subprocessors (AWS US, GCP US) fall under the Cloud Act. For strictly European processing, CaptainDNS is the simplest option.

Logs and retention

Individual checks are kept for 30 days, then automatically deleted. Aggregated metrics (monthly uptime, average latency) are kept for 12 months. You can delete a monitor at any time, which wipes all its associated data within 24 hours.

Compliant by default

No consent to collect from your users: monitoring is an internal processing activity for which you are the data controller. CaptainDNS acts as a processor under article 28 of GDPR. The DPA is available on request.

Frequently asked questions about monitoring

Q: What is website monitoring?

A: Website monitoring is the practice of continuously checking the availability, latency, and integrity of an HTTP URL. A monitoring tool sends a request at a regular interval (for example every 5 minutes), records the response, and triggers an alert on failure. This lets you catch an outage before your users do.

Q: How often does CaptainDNS check my URL?

A: By default, CaptainDNS runs an HTTP check every 5 minutes on each of your monitors. You can customize the frequency with a cron expression for advanced scenarios (check every minute during business hours, exclude a maintenance window, and so on).

Q: How do I receive an alert when my site goes down?

A: When you create the monitor, set a recipient email address. The moment a check fails (5xx code, timeout, DNS error, invalid TLS certificate), you get a real-time email alert. CaptainDNS groups alerts to avoid flooding your inbox.

Q: What does 99.9% uptime mean?

A: 99.9% uptime means your service is available 99.9% of the time, which translates to roughly 8 hours and 45 minutes of maximum downtime per year (43 minutes per month). It is the standard threshold for a production site. At 99.99%, you drop to 52 minutes of downtime per year.

Q: Is CaptainDNS free for monitoring my site?

A: Yes. The free plan includes 5 HTTP monitors with checks every 5 minutes, unlimited email alerts, a 30-day heatmap, and p95 latency. No credit card required at sign-up, no limited trial period.

Q: What is the difference between CaptainDNS and UptimeRobot?

A: CaptainDNS combines DNS, SPF, DKIM, DMARC, blacklists, and HTTP monitoring in a single dashboard, hosted in the EU and GDPR compliant. UptimeRobot only does uptime monitoring and stores its data in the United States. CaptainDNS offers 5 free monitors, compared to 50 on UptimeRobot but with a check every 5 minutes (identical to the UptimeRobot free plan).

Q: Can I monitor an authenticated URL or a private endpoint?

A: Yes for public URLs reachable from the internet. CaptainDNS supports custom HTTP headers (Authorization, X-API-Key) to query token-protected endpoints. URLs behind a VPN or a private firewall are not reachable from our probes.

Q: How do I share my monitoring results?

A: CaptainDNS offers an integration with public status pages. Link your HTTP monitor to a public status page to expose uptime, latency, and incident history to your users or customers without giving them access to your private dashboard.

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