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Built-in metrics
Every k6 test emits built-in and 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:
| Metric Name | Type | Description |
|---|---|---|
| checks | Rate | The rate of successful checks. |
| data_received | Counter | The amount of received data. This example covers how to track data for an individual URL. |
| data_sent | Counter | The amount of data sent. Track data for an individual URL to track data for an individual URL. |
| dropped_iterations | 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 for more details. |
| iteration_duration | 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. |
| iterations | Counter | The aggregate number of times the VUs execute the JS script (the default function). |
| vus | Gauge | Current number of active virtual users |
| vus_max | Gauge | Max possible number of virtual users (VU resources are pre-allocated, 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 allhttp_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.
| Metric Name | Type | Description |
|---|---|---|
| http_req_blocked | Trend | Time spent blocked (waiting for a free TCP connection slot) before initiating the request. float |
| http_req_connecting | Trend | Time spent establishing TCP connection to the remote host. float |
| http_req_duration | 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 | The rate of failed requests according to setResponseCallback. |
| http_req_receiving | Trend | Time spent receiving response data from the remote host. float |
| http_req_sending | Trend | Time spent sending data to the remote host. float |
| http_req_tls_handshaking | Trend | Time spent handshaking TLS session with remote host |
| http_req_waiting | Trend | Time spent waiting for response from remote host (a.k.a. “time to first byte”, or “TTFB”). float |
| http_reqs | Counter | How many total HTTP requests k6 generated. |
Browser metrics
The k6 browser module emits its own metrics based on the Core Web Vitals.
These core metrics will evolve over time when technology changes, but for now, k6 tracks the following core web vitals:
| 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 for more information. |
| browser_web_vital_fid | Measures the responsiveness of a web page by quantifying the delay between a user’s first interaction, such as clicking a button, and the browser’s response. Refer to First Input Delay 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 for more information. |
Other Web Vitals
Apart from the Core Web Vitals, the browser module also reports Other Web Vitals.
| 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 for more information. |
| browser_web_vital_inp | An experimental metric that measures a page’s responsiveness. Refer to Interaction to Next Paint 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 for more information. |
Built-in WebSocket metrics
k6 emits the following metrics when interacting with a WebSocket service through the experimental or legacy websockets API.
| Metric name | Type | Description |
|---|---|---|
| ws_connecting | Trend | Total duration for the WebSocket connection request. |
| ws_msgs_received | Counter | Total number of messages received |
| ws_msgs_sent | Counter | Total number of messages sent |
| ws_ping | Trend | Duration between a ping request and its pong reception |
| ws_session_duration | Trend | Duration of the WebSocket session. Time between the start of the connection and the end of the VU execution. |
| ws_sessions | 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 API.
| Metric Name | Type | Description |
|---|---|---|
| grpc_req_duration | Trend | Time to receive response from remote host |
| grpc_streams | Counter | Total number of started streams |
| grpc_streams_msgs_received | Counter | Total number of messages received |
| grpc_streams_msgs_sent | Counter | Total number of messages sent |
Note
Steams-related metrics (grpc_streams*) are available only onk6version0.49.0or higher or when using thek6/experimental/grpcmodule, which is available onk6version0.45.0.
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