--- title: "Built-in metrics | Grafana k6 documentation" description: "A reference of built-in metrics for different supported protocols." --- # Built-in metrics Every k6 test emits built-in and [custom metrics](/docs/k6/latest/using-k6/metrics/create-custom-metrics/). Each supported protocol also has its specific metrics. ## Standard built-in metrics k6 always collects the following metrics, no matter what protocol the test uses: Expand table | Metric Name | Type | Description | |---------------------|---------------------------------------------------------------|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------| | checks | [Rate](/docs/k6/latest/javascript-api/k6-metrics/rate/) | The rate of successful checks. In the end-of-test summary, this metric is displayed as three values: `checks_total` (Counter), `checks_succeeded` (Rate), and `checks_failed` (Rate). These display values are not emitted to output backends and cannot be used in thresholds. | | data\_received | [Counter](/docs/k6/latest/javascript-api/k6-metrics/counter/) | The amount of received data. [This example covers how to track data for an individual URL](/docs/k6/latest/examples/track-transmitted-data-per-url/). | | data\_sent | [Counter](/docs/k6/latest/javascript-api/k6-metrics/counter/) | The amount of data sent. [Track data for an individual URL](/docs/k6/latest/examples/track-transmitted-data-per-url/) to track data for an individual URL. | | dropped\_iterations | [Counter](/docs/k6/latest/javascript-api/k6-metrics/counter/) | The number of iterations that weren’t started due to lack of VUs (for the arrival-rate executors) or lack of time (expired maxDuration in the iteration-based executors). Refer to [Dropped iterations](/docs/k6/latest/using-k6/scenarios/concepts/dropped-iterations/) for more details. | | iteration\_duration | [Trend](/docs/k6/latest/javascript-api/k6-metrics/trend/) | The time to complete one full iteration, including time spent in `setup` and `teardown`. To calculate the duration of the iteration’s function for the specific scenario, [try this workaround](/docs/k6/latest/using-k6/workaround-iteration-duration/). | | iterations | [Counter](/docs/k6/latest/javascript-api/k6-metrics/counter/) | The aggregate number of times the VUs execute the JS script (the `default` function). | | vus | [Gauge](/docs/k6/latest/javascript-api/k6-metrics/gauge/) | Current number of active virtual users | | vus\_max | [Gauge](/docs/k6/latest/javascript-api/k6-metrics/gauge/) | Max possible number of virtual users (VU resources are [pre-allocated](/docs/k6/latest/using-k6/scenarios/concepts/arrival-rate-vu-allocation/), to avoid affecting performance when scaling up load). | ## HTTP-specific built-in metrics These metrics are generated only when the test makes HTTP requests. > Note > > For all `http_req_*` metrics, **the timestamp is emitted the end of the request.** In other words, the timestamp happens when k6 receives the end of the response body, or the request times out. Expand table | Metric Name | Type | Description | |-----------------------------|---------------------------------------------------------------|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------| | http\_req\_blocked | [Trend](/docs/k6/latest/javascript-api/k6-metrics/trend/) | Time spent blocked (waiting for a free TCP connection slot) before initiating the request. `float` | | http\_req\_connecting | [Trend](/docs/k6/latest/javascript-api/k6-metrics/trend/) | Time spent establishing TCP connection to the remote host. `float` | | http\_req\_duration | [Trend](/docs/k6/latest/javascript-api/k6-metrics/trend/) | Total time for the request. It’s equal to `http_req_sending + http_req_waiting + http_req_receiving` (i.e. how long did the remote server take to process the request and respond, without the initial DNS lookup/connection times). `float` | | http\_req\_failed | [Rate](/docs/k6/latest/javascript-api/k6-metrics/rate/) | The rate of failed requests according to [setResponseCallback](/docs/k6/latest/javascript-api/k6-http/set-response-callback/). | | http\_req\_receiving | [Trend](/docs/k6/latest/javascript-api/k6-metrics/trend/) | Time spent receiving response data from the remote host. `float` | | http\_req\_sending | [Trend](/docs/k6/latest/javascript-api/k6-metrics/trend/) | Time spent sending data to the remote host. `float` | | http\_req\_tls\_handshaking | [Trend](/docs/k6/latest/javascript-api/k6-metrics/trend/) | Time spent handshaking TLS session with remote host | | http\_req\_waiting | [Trend](/docs/k6/latest/javascript-api/k6-metrics/trend/) | Time spent waiting for response from remote host (a.k.a. “time to first byte”, or “TTFB”). `float` | | http\_reqs | [Counter](/docs/k6/latest/javascript-api/k6-metrics/counter/) | How many total HTTP requests k6 generated. | ## Browser metrics The [k6 browser module](/docs/k6/latest/using-k6-browser/) emits its own metrics based on the [Core Web Vitals](https://web.dev/vitals/#core-web-vitals). These core metrics will evolve over time when technology changes, but for now, k6 tracks the following core web vitals: Expand table | Metric name | Description | |--------------------------|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------| | browser\_web\_vital\_cls | Measures the visual stability on a webpage by quantifying the amount of unexpected layout shift of visible page content. Refer to [Cumulative Layout Shift](https://web.dev/cls/) for more information. | | browser\_web\_vital\_inp | A metric that measures a page’s responsiveness. Refer to [Interaction to Next Paint](https://web.dev/inp/) for more information. | | browser\_web\_vital\_lcp | Measures the time it takes for the largest content element on a page to become visible. Refer to [Largest Contentful Paint](https://web.dev/lcp/) for more information. | ### Other Web Vitals Apart from the Core Web Vitals, the browser module also reports [Other Web Vitals](https://web.dev/vitals/#other-web-vitals). Expand table | Metric name | Description | |---------------------------|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------| | browser\_web\_vital\_fcp | Measures the time it takes for the browser to render the first DOM element on the page, whether that’s a text, image or header. Refer to [First Contentful Paint](https://web.dev/fcp/) for more information. | | browser\_web\_vital\_ttfb | Measures the time it takes between the browser request and the start of the response from a server. Refer to [Time to First Byte](https://web.dev/ttfb/) for more information. | ## Built-in WebSocket metrics `k6` emits the following metrics when interacting with a WebSocket service through the [`k6/websockets`](/docs/k6/latest/javascript-api/k6-websockets/) or legacy `k6/ws` API. Expand table | Metric name | Type | Description | |-----------------------|---------------------------------------------------------------|--------------------------------------------------------------------------------------------------------------| | ws\_connecting | [Trend](/docs/k6/latest/javascript-api/k6-metrics/trend/) | Total duration for the WebSocket connection request. | | ws\_msgs\_received | [Counter](/docs/k6/latest/javascript-api/k6-metrics/counter/) | Total number of messages received | | ws\_msgs\_sent | [Counter](/docs/k6/latest/javascript-api/k6-metrics/counter/) | Total number of messages sent | | ws\_ping | [Trend](/docs/k6/latest/javascript-api/k6-metrics/trend/) | Duration between a ping request and its pong reception | | ws\_session\_duration | [Trend](/docs/k6/latest/javascript-api/k6-metrics/trend/) | Duration of the WebSocket session. Time between the start of the connection and the end of the VU execution. | | ws\_sessions | [Counter](/docs/k6/latest/javascript-api/k6-metrics/counter/) | Total number of started WebSocket sessions. | ## Built-in gRPC metrics k6 emits the following metrics when it interacts with a service through the [`gRPC`](/docs/k6/latest/javascript-api/k6-net-grpc/) API. Expand table | Metric Name | Type | Description | |-------------------------------|---------------------------------------------------------------|-------------------------------------------| | grpc\_req\_duration | [Trend](/docs/k6/latest/javascript-api/k6-metrics/trend/) | Time to receive response from remote host | | grpc\_streams | [Counter](/docs/k6/latest/javascript-api/k6-metrics/counter/) | Total number of started streams | | grpc\_streams\_msgs\_received | [Counter](/docs/k6/latest/javascript-api/k6-metrics/counter/) | Total number of messages received | | grpc\_streams\_msgs\_sent | [Counter](/docs/k6/latest/javascript-api/k6-metrics/counter/) | Total number of messages sent | > Note > > Steams-related metrics (`grpc_streams*`) are available only on `k6` version `0.49.0` or higher or when using the `k6/experimental/grpc` module, which is available on `k6` version `0.45.0`.