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Checkly tracks a comprehensive set of metrics across all check types to provide insights into the performance, reliability, and user experience of your applications and services. This page explains common metrics, what they measure, and which check types support them.

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Response Time Metrics

Response time metrics measure how quickly your services respond to requests, providing crucial insights into performance and user experience.

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Average Response Time

What it measures: The arithmetic mean response time across all check executions within the selected time period. Unit: Milliseconds
Available for: API, Browser, TCP, DNS, Multistep, URL checks, Playwright Check Suites
  • Establishing performance baselines
  • Detecting performance degradation trends
  • Comparing performance across different time periods
  • Setting SLA thresholds

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95th Percentile Response Time (P95)

What it measures: The response time value below which 95% of all requests fall. This metric filters out the slowest 5% of requests to give you a more realistic view of typical user experience. Unit: Milliseconds
Available for: API, Browser, TCP, DNS, Multistep, URL checks, Playwright Check Suites
  • SLA monitoring and compliance
  • Performance budgeting
  • Capacity planning
  • Identifying performance outliers

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99th Percentile Response Time (P99)

What it measures: The response time value below which 99% of all requests fall. This metric helps identify the worst-case performance experienced by users. Unit: Milliseconds
Available for: API, Browser, TCP, DNS, Multistep, URL checks, Playwright Check Suites
  • Understanding worst-case user experience
  • Setting performance alerts for edge cases
  • Optimizing for the most demanding scenarios

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Median Response Time (P50)

What it measures: The middle value of all response times when sorted from fastest to slowest. Half of all requests complete faster than this time, and half complete slower. Unit: Milliseconds
Available for: API, Browser, TCP, DNS, Multistep, URL checks, Playwright Check Suites
  • Understanding typical user experience
  • Baseline performance monitoring
  • Comparing with average response time to identify skewed distributions
  • Performance trend analysis

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Minimum Response Time

What it measures: The fastest response time recorded during the selected time period. Unit: Milliseconds
Available for: API, Browser, TCP, DNS, Multistep, URL checks, Playwright Check Suites
  • Understanding best-case performance
  • Capacity planning for optimal conditions
  • Performance optimization validation
  • Network latency analysis

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Maximum Response Time

What it measures: The slowest response time recorded during the selected time period. Unit: Milliseconds
Available for: API, Browser, TCP, DNS, Multistep, URL checks, Playwright Check Suites
  • Identifying performance spikes
  • Troubleshooting worst-case scenarios
  • Setting timeout thresholds
  • Performance regression detection

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Success Rate Metrics

Success rate metrics measure the reliability and availability of your services.

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Success Rate

What it measures: The percentage of check executions that completed successfully according to the defined success criteria (e.g., HTTP 2xx status codes, successful script execution). Unit: Percentage (0-100%)
Available for: API, Browser, Heartbeat, ICMP, TCP, Multistep, URL checks, Playwright Check Suites
  • SLA compliance monitoring
  • Service reliability tracking
  • Availability reporting
  • Alerting on service degradation

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Web Vitals (Browser-Specific)

Core Web Vitals are a set of metrics defined by Google that measure real-world user experience for loading performance, interactivity, and visual stability.
Playwright Check Suites also collect Web Vitals (LCP, CLS, INP, FCP, TTFB and TBT) for each page visit. They appear in the test report (beta) but aren’t available as aggregated metrics yet.

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First Contentful Paint (FCP)

What it measures: The time from when the page starts loading to when any part of the page’s content is rendered on the screen. Unit: Milliseconds
Available for: Browser checks only Google’s thresholds:
  • Good: ≤ 1.8 seconds
  • Needs improvement: 1.8 - 3.0 seconds
  • Poor: > 3.0 seconds

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Largest Contentful Paint (LCP)

What it measures: The time from when the page starts loading to when the largest text block or image element is rendered. Unit: Milliseconds
Available for: Browser checks only Google’s thresholds:
  • Good: ≤ 2.5 seconds
  • Needs improvement: 2.5 - 4.0 seconds
  • Poor: > 4.0 seconds

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Cumulative Layout Shift (CLS)

What it measures: A measure of how much visible content shifts during the loading process. Lower scores indicate better visual stability. Unit: Score (0-1+)
Available for: Browser checks only Google’s thresholds:
  • Good: ≤ 0.1
  • Needs improvement: 0.1 - 0.25
  • Poor: > 0.25

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Total Blocking Time (TBT)

What it measures: The time a page is “blocked” from receiving user input because the main rendering thread is busy. A high TBT means users experience sluggish behavior when interacting with your page. Unit: Milliseconds
Available for: Browser checks only

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Time to First Byte (TTFB)

What it measures: How long it took your server to respond with the first byte of content when the browser requested the page. TTFB varies by location: requesting a page hosted in the US from Japan gives a higher TTFB. Unit: Milliseconds
Available for: Browser checks only

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ICMP-Specific Metrics

These metrics are specific to ICMP monitors, which verify host reachability and measure network performance using ICMP Echo Requests (pings).

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Average Ping Latency

What it measures: The average round-trip time (RTT) across all received ICMP Echo Reply packets within a check run. Unit: Milliseconds
  • Establishing network latency baselines
  • Detecting latency degradation over time
  • Comparing latency across regions

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Minimum Ping Latency

What it measures: The fastest round-trip time recorded across all received packets within a check run. Unit: Milliseconds
  • Understanding best-case network performance

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Maximum Ping Latency

What it measures: The slowest round-trip time recorded across all received packets within a check run. Unit: Milliseconds
  • Identifying latency spikes
  • Setting timeout and alerting thresholds

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Ping Latency Standard Deviation

What it measures: The variability of round-trip times across all received packets within a check run. Higher values indicate less consistent network performance (jitter). Unit: Milliseconds
  • Measuring network stability and jitter

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Packet Loss

What it measures: The percentage of ICMP Echo Request packets that did not receive a reply. Unit: Percentage (0-100%)

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P95 Ping Latency

What it measures: The 95th percentile of average ping latency across check runs within the selected time period. Unit: Milliseconds
  • SLA monitoring for network latency
  • Filtering out outlier spikes for a realistic performance view

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P95 Packet Loss

What it measures: The 95th percentile of packet loss across check runs within the selected time period. Unit: Percentage (0-100%)
  • SLA monitoring for packet delivery
  • Identifying persistent vs. intermittent packet loss

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Additional Metrics by Check Type

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TCP Connection Time

What it measures: The time required to establish a TCP connection to the target host and port. Unit: Milliseconds
Available for: API, URL, TCP, gRPC checks
  • Network connectivity monitoring
  • Port availability testing
  • Network latency analysis
  • Infrastructure health monitoring

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DNS Resolution Time

What it measures: The time required to resolve the hostname to an IP address via DNS lookup. Unit: Milliseconds
Available for: API, URL, TCP, gRPC checks. ICMP monitors also show the DNS resolution time on each check result.
  • DNS performance monitoring
  • Network troubleshooting
  • Infrastructure optimization
  • Geographic performance analysis

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SSL Handshake Time

What it measures: The time required to complete the SSL/TLS handshake process for secure connections. Unit: Milliseconds
Available for: SSL monitors only
  • SSL/TLS performance monitoring
  • Certificate validation timing
  • Security overhead analysis
  • HTTPS optimization
For all available metrics see the Analytics API Reference.