Availability monitoring tools: website availability monitoring, server and application availability monitoring compared

Short answer: availability monitoring answers a different question from uptime monitoring. Uptime asks whether the machine is running. Availability asks whether a user could actually complete the request, which is why it is measured from outside your network and why it is almost always lower than your uptime number. Pick the tool by the layer you have to prove: external HTTP checks with response assertions for website and application availability, agent or SNMP polling for server and network availability, and a full-stack platform only when you also need to know why it broke. Eight tools are compared below on layer, fastest interval, what they can assert on, and real US dollar list prices.

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Last updated September 2026 · US dollar list prices

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the distinction that matters

What is the difference between uptime and availability?

Uptime is a property of a machine: it is powered on and answering. Availability is a property of a service: a real request from a real place succeeded inside an acceptable time. A server can be up for a full month and still be unavailable for hours, and every incident review that starts with "but the box never went down" is that gap in action.

This is not a semantic argument. It decides what you buy. A tool that only pings a host reports uptime. A tool that requests the URL a customer requests, checks the status code, checks that the body contains what it should, and checks that the response arrived inside a budget, reports availability. Those two numbers routinely differ by a fraction of a percent, which is exactly the range every SLA lives in.

Failure	Host reachable	Counts as unavailable	Needs
Power or network loss	No	Yes	Any ping check
Application process crashed	Yes	Yes	HTTP check
HTTP 500 from a bad deploy	Yes	Yes	Status code assertion
Expired TLS certificate	Yes	Yes, browsers refuse	SSL expiry check
Database down, page renders an error	Yes	Yes	Keyword assertion
Login returns 200 with an empty session	Yes	Yes	JSON path assertion
Page takes 14 seconds to answer	Yes	Usually yes	Response time budget
DNS record deleted	Yes, by IP	Yes	External check by hostname
Region-specific routing failure	Yes, from your office	Yes, for some users	Multi-region checks

Eight of those nine rows leave the host reachable. That is the whole case for buying an availability tool rather than a ping tool, and it is why availability is measured externally.

A worked example

A deploy at 02:14 puts a checkout endpoint into a 500 loop. Someone notices at 02:36 and rolls back. The host answered ICMP the entire time and its operating system never restarted, so infrastructure uptime for the month reads 100.00000%.

Measured as availability, those 22 minutes are 22 of the 43,833 minutes in an average month, so checkout availability reads 99.94981%. If you sold a 99.9% SLA you are still inside it, with 21 minutes and 50 seconds of budget left. If you sold 99.99% you blew through a 4 minute 23 second budget five times over, and the uptime dashboard would never have told you.

The short version

Uptime is what your infrastructure team measures. Availability is what your customer experiences and what your contract commits to. Buy the tool that measures the second one, then use the first for capacity work.

the comparison

Eight availability monitoring tools, side by side

The column most people skip is the second one. A tool built for network availability polls devices you own from inside your own network, and it cannot tell you whether a customer in Chicago could load your checkout page. A tool built for service availability runs outside and cannot tell you which switch port flapped. Buying the wrong layer is the most common and most expensive mistake in this category.

Tool	Layer it measures	Fastest interval	Assertions beyond status	Entry price (USD list)	Best for
AlertPing	Website, API, port, service	30 seconds on Team and above, 60 seconds on entry	Keyword, JSON path, response time budget	$19/mo for 20 monitors at 60 seconds, $59/mo for 30-second checks	Proving service availability against an SLA on a flat bill
UptimeRobot	Website, port, heartbeat	60 seconds on Solo, 30 seconds on Team	Keyword matching only	Free for 50 monitors at 5 minutes, Solo about $9/mo billed annually	Basic availability on the smallest possible budget
StatusCake	Website, domain, SSL, page speed	1 minute on Superior, 30 seconds on Business	Keyword and status assertions	Free for 10 tests, Superior $24.49/mo, Business $79.99/mo	Bundling availability with domain and page speed checks
Better Stack	Website, API, heartbeat, on-call	3 minutes free, 30 seconds paid	Keyword and status assertions	Free for 10 monitors, then about $25/mo per 50 monitors	Availability plus on-call scheduling in one product
Pingdom	Website, transaction, real user	1 minute at every tier	Yes, plus scripted transaction checks	$1 per uptime check per month, so $10 for 10 checks	Scripted checkout journeys and RUM alongside availability
Site24x7	Website, server agent, network device	1 minute, 30 seconds only on Enterprise Plus	Yes, including multi-step API sequences	Free tier, web uptime from about $10/mo	One vendor across service, server and network layers
Dynatrace	Full stack, host, application, synthetic	1 minute	Yes, plus traces and root cause analysis	Consumption: $29/mo per host infrastructure, $0.001 per synthetic request	Enterprises that need the cause, not just the outage
ManageEngine OpManager	Network device and server availability, on premises	1 minute, configurable per device	SNMP, WMI and device thresholds	Free up to 3 devices, paid editions quoted by device count	Availability of switches, routers and internal servers

Prices are US dollar list, read in September 2026. Third party listings for OpManager disagree with each other by a wide margin, quoting anywhere from about $245 to about $795 for an entry edition, so treat it as a quoted product and get the number in writing for your device count. The full pricing comparison for the service-layer tools is on uptime monitoring pricing.

pick your layer

The four layers availability monitoring tools actually cover

Almost every disappointing purchase in this category comes from buying at the wrong layer. These are the four, what each one proves, and what each one is blind to.

Layer 1

Network availability monitoring

Polls switches, routers, firewalls and links over SNMP or ICMP from inside your network. Proves the path exists and the interface is up. Tools: OpManager, PRTG, Zabbix, Site24x7 network add-ons. Blind to everything above layer 4, so a perfectly healthy network graph is compatible with a completely broken application.

Layer 2

Server availability monitoring

Agents or remote checks that confirm the host is alive and that CPU, memory and disk are inside thresholds. Proves the machine can serve. Tools: Datadog, Site24x7, Dynatrace, and any RMM suite. Blind to application logic, and blind to whether anyone outside your data center can reach the box at all.

Layer 3

Application availability monitoring

External HTTP requests against the URLs and endpoints your users hit, asserting on status code, body content and response time. This is the layer that matches what a customer experiences and the layer an SLA is written against. Tools: AlertPing, UptimeRobot, Better Stack, StatusCake, Pingdom. Blind to the root cause, on purpose.

Layer 4

User journey availability monitoring

Scripted browser sessions that log in, add to cart and check out, asserting each step. The only layer that catches a broken payment form that returns 200 on every request. Tools: Pingdom transaction checks, Datadog browser tests, Checkly, Dynatrace. Costs an order of magnitude more per check and the scripts break every time the UI changes.

Most teams need layer 3 first and cannot justify layer 4 until a checkout flow has failed silently at least once. If you run internal hardware as well, layer 1 and layer 3 are complementary rather than competing, and buying one vendor for both usually means accepting a slower interval on the part that faces customers. Our own coverage of layer 2 is external only and is described on server monitoring.

the number nobody publishes

Your check interval sets the smallest outage you can prove

Availability is computed from the checks you ran, so a single failed check is the smallest unit of downtime your tool can record. That gives every interval a hard resolution limit, and it decides which SLA numbers you can evidence at all. An average month is 43,833 minutes, which is 30.44 days, and every figure below comes from that.

Check interval	Smallest outage recordable	Best reading below 100%	Failed checks inside a 99.9% budget	Failed checks inside a 99.99% budget
5 minutes	5 minutes	99.98859%	8.8	0.9
1 minute	1 minute	99.99772%	43.8	4.4
30 seconds	30 seconds	99.99886%	87.7	8.8
15 seconds	15 seconds	99.99943%	175.3	17.5

Read the last column first

A 99.99% availability target allows 4 minutes and 23 seconds of downtime a month. On a five-minute interval, one failed check already exceeds that. You literally cannot record a 99.99% month that contains a single failure, so the target is unmeasurable at that interval.

Detection lag is separate and also halves

On top of resolution, you find out about an outage roughly half an interval after it starts. Five minutes hides about two and a half minutes on average, 30 seconds hides about 15. That lag is real downtime your customers had and your dashboard did not.

Faster is not free of noise

A faster interval also multiplies transient blips. That is why confirmation matters more than raw speed: AlertPing re-tests every failure from Frankfurt, Virginia and Singapore before it alerts, so a single bad packet from one region does not become a page.

If you are choosing an availability target rather than a tool, the downtime allowance behind each number is worked through in what is a good uptime percentage, and the reporting side is covered on SLA monitoring software.

buying criteria

Six questions to settle before you buy availability monitoring software

Where does the check run from

A checker that lives inside the environment it watches goes dark with it. That is the honest cost of self-hosting Zabbix or Uptime Kuma on the same cluster. If the number is going into a customer contract, it has to be measured from outside.

What is it allowed to assert on

Status code only, keyword, JSON path, or a full script. Six of the nine failures in the table above return a 200, so a status-only check will report availability that your customers would dispute. Ask this before you ask about price.

Does it confirm before it pages

One failed request from one location is usually a network blip. Tools that re-check from additional regions before alerting cut false pages sharply, and a team that trusts its alerts responds faster than one that has learned to ignore them.

Can it produce the report

If availability is contractual, you need a per-period figure you can send to a customer, with maintenance windows excluded. Plenty of tools show a dashboard and cannot export a defensible monthly number. Ours are on the Business plan.

How is alerting metered

SMS sold as credits runs out during exactly the long incident where you need it. Check whether text and voice are included or bundled, because that detail moves the real annual cost more than the headline plan price.

Flat or metered billing

Consumption pricing is cheap at low frequency and punishing at high. A single one-minute HTTP monitor is 43,833 executions a month, which on Dynatrace list rates is $43.83 for one URL from one location. Flat plans cost more at tiny scale and far less at real coverage.

where each one wins

Which availability monitoring tool is right for which team

AlertPing

Built for teams whose availability number ends up in a contract or a board deck. Checks run against sites, APIs and ports, assert on status code, a keyword, a JSON path and a response time budget, and every failure is re-tested from three regions before anyone is woken. SMS, email, Slack and webhook alerts are on every plan rather than sold as credits. Pricing is flat from $19 a month for 20 monitors at 60-second checks, with 30-second checks from $59.

Where it loses: there is no free plan, no server agent, no SNMP and no network device discovery, so layers 1 and 2 are out of scope. There are no scripted browser journeys, so a broken checkout that returns 200 at every step will not be caught. No APM, no tracing, no real user monitoring.

UptimeRobot

The cheapest credible way to start. The free tier covers 50 monitors at five-minute checks, which per the table above is enough to evidence 99.9% but not 99.99%. Solo is about $9 a month billed annually at 60-second checks and Team about $38 at 30 seconds, so they match us on interval and beat us on entry price.

Where it loses: assertions stop at keyword matching, so a 200 with a malformed payload passes. The free tier excludes SSL monitoring and is non-commercial.

Site24x7 and ManageEngine OpManager

Both from Zoho, and between them the widest layer coverage on this page. Site24x7 spans website checks, server agents, network devices and APM in one console, from about $10 a month for web uptime. OpManager is the on-premises network product, free for three devices and quoted by device count above that, and it is the right answer when the thing you must prove available is a switch stack rather than a checkout page.

Where they lose: Site24x7 gates 30-second polling behind its top Enterprise Plus tier, so the fast interval that matters for a customer-facing SLA is expensive. Breadth also brings a console most small teams never finish configuring.

Dynatrace and Datadog

Buy these when the question is why, not whether. Both give you traces, host metrics and synthetic checks in one place, and both are genuinely excellent at root cause. Dynatrace infrastructure monitoring is $29 a month per host and synthetic HTTP requests are $0.001 each.

Where they lose for this job: both floor at a one-minute check interval at any price, so neither can evidence availability at a finer resolution than one minute, and the metered synthetic rate makes broad URL coverage expensive. The full breakdown is on Datadog vs Dynatrace, and every vendor's per-execution rate is set side by side in our synthetic monitoring tools comparison.

Pingdom

The strongest of the mainstream tools at layer 4. Scripted transaction checks walk a real journey and assert each step, which is the only reliable way to catch a checkout that fails silently. Pricing is a flat $1 per uptime check a month at every volume.

Where it loses: one minute is the floor on every tier, there is no free plan, and the per-check rate never falls, so at 500 URLs the list price is $500 a month. The full rate card is in how much Pingdom costs.

Better Stack and StatusCake

Better Stack pairs availability checks with on-call scheduling and incident management, which is worth real money if you would otherwise buy a separate paging product. StatusCake bundles domain expiry and page speed alongside availability, which no other tool here does at that price, at $24.49 a month for Superior.

Where they lose: Better Stack's free tier checks every three minutes, and its modular pricing means monitors, seats and status pages are billed as separate blocks. StatusCake keeps 30-second checks on its $79.99 Business plan.

questions buyers ask

Availability monitoring, answered

What is availability monitoring?

Availability monitoring is the automated, repeated verification that a service can actually serve a request, run from outside the environment that hosts it. It differs from uptime monitoring because it asserts on the response, not just on the fact that something answered, and it produces the percentage figure that service level agreements are written against.

What are availability monitoring tools?

They are services that run scheduled checks against your sites, endpoints, servers or network devices and record every failure as measured downtime. The service-layer ones are AlertPing, UptimeRobot, StatusCake, Better Stack, Pingdom and Site24x7. The infrastructure-layer ones are OpManager, PRTG, Zabbix, Datadog and Dynatrace. They are not interchangeable.

How do you monitor application availability?

Request the URL a user would request, from outside your network, on a fixed interval. Assert the exact status code you expect rather than anything under 400, assert on one value that only exists when the request truly succeeded, and set a response time budget. Then route failures to a channel a human answers at night.

How is availability calculated?

Availability is uptime divided by total time in the period, expressed as a percentage. Using an average month of 43,833 minutes, 22 minutes of downtime is 99.94981%. Most tools compute it from failed checks rather than from wall clock time, which is why your check interval sets the resolution of the answer.

What is a good availability monitoring interval in minutes?

One minute or faster for anything that earns revenue, five minutes for internal services nobody is paged for. The deciding factor is the target: a 99.99% commitment allows 4 minutes 23 seconds of downtime a month, which a five-minute interval cannot resolve, so a five-minute check makes that number unprovable.

What is network availability monitoring?

It is polling network devices, switches, routers, firewalls and links, over SNMP or ICMP to confirm each is reachable and its interfaces are up. It runs inside your own network, which makes it excellent for finding the failed hop and useless for proving that a customer on the public internet could reach your service.

Is availability monitoring the same as APM?

No. Availability monitoring tells you a service stopped working and when. Application performance monitoring tells you which query, dependency or code path made it slow. They answer different questions and most mature teams run both, with the availability tool owning the page and the APM owning the investigation.

Are there free availability monitoring tools?

Yes. UptimeRobot covers 50 monitors at five-minute checks, StatusCake covers 10 tests, Better Stack covers 10 monitors at three minutes, and Zabbix and Uptime Kuma are free to self-host. All of them trade interval, escalation or independence, and a self-hosted checker inside the environment it watches cannot report on its own outage.

the option already in your bill

Your cloud provider already sells availability monitoring

Before you buy a tool, check what you are already entitled to. All three large US clouds ship an availability checker, all three bill it as metered consumption rather than a flat plan, and all three share a limitation that matters more than the price: the check runs on the same platform it is measuring, so it cannot be independent evidence of that platform's availability.

The pricing shape is worth understanding because it inverts as you grow. Metered checks are genuinely cheap for one or two endpoints and get expensive fast, since you pay per request per location and vendors recommend five locations minimum. Azure's Application Insights standard tests list at $0.0005 per execution in East US, so Microsoft's own default of a five minute frequency across five locations is 43,833 executions and $21.92 a month for a single URL. Ten URLs at that default is $219.16. That is the crossover most teams hit without noticing.

Google Cloud is the one people misread, because its free allowance is quoted as 1 million executions a month and that sounds like it covers everything. It does not, because each checker region bills separately. One URL at the default 60 second period across the three USA checkers is 131,499 executions, so the free million runs out at 7.6 URLs, and each URL past that is $39.45 a month at $0.30 per 1,000.

Microsoft Azure

Application Insights availability tests

Billed per execution per location, with a five minute default frequency at each location. The classic URL ping tests retire on September 30, 2026 and are removed from your resources on that date, so anyone still relying on one has a hard deadline. Full rate card and the migration steps are on Azure uptime monitoring.

Amazon Web Services

CloudWatch Synthetics and Route 53 health checks

Canaries run as Lambda functions inside a region you choose, and Route 53 health checks cannot notify anyone until you wire them to a CloudWatch alarm and an SNS topic. What each one costs, and what neither can tell you, is on AWS uptime monitoring.

Google Cloud

Cloud Monitoring uptime checks

Free up to 1 million executions per project, but every checker region bills separately, so the allowance covers 7.6 URLs at the default 60 second period. The period options stop at 60 seconds, with nothing faster at any price. The full arithmetic is on GCP uptime monitoring.

Measure availability the way your contract defines it

AlertPing checks sites, APIs and ports as often as every 30 seconds, asserts on status code, keyword, JSON path and response time, and confirms every failure from Frankfurt, Virginia and Singapore before it alerts you. Flat plans from $19 a month, with 30-second checks from $59.

See pricing

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