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 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.
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
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 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.