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JSON

You can also make k6 output detailed statistics in JSON format by using the --out/-o option for k6 run, like this:

k6 run --out json=my_test_result.json script.js

The JSON file will contain lines like these:

{"type":"Metric","data":{"type":"gauge","contains":"default","tainted":null,"thresholds":[],"submetrics":null},"metric":"vus"}
{"type":"Point","data":{"time":"2017-05-09T14:34:45.625742514+02:00","value":5,"tags":null},"metric":"vus"}
{"type":"Metric","data":{"type":"trend","contains":"time","tainted":null,"thresholds":["avg\u003c1000"],"submetrics":null},"metric":"http_req_duration"}
{"type":"Point","data":{"time":"2017-05-09T14:34:45.239531499+02:00","value":459.865729,"tags":{"group":"::my group::json","method":"GET","status":"200","url":"https://httpbin.org/get"}},"metric":"http_req_duration"}

Each line will either contain information about a metric, or log a data point (sample) for a metric. Lines consist of three items:

  • type - can have the values Metric or Point where Metric means the line is declaring a metric, and Point is an actual data point (sample) for a metric.
  • data - is a dictionary that contains lots of stuff, varying depending on the "type" above.
  • metric - the name of the metric.

Metric

This line contains information about the nature of a metric. Here, "data" will contain the following:

  • "type" - the metric type ("gauge", "rate", "counter" or "trend")
  • "contains" - information on the type of data collected (can e.g. be "time" for timing metrics)
  • "tainted" - has this metric caused a threshold to fail?
  • "threshold" - are there any thresholds attached to this metric?
  • "submetrics" - any derived metrics created as a result of adding a threshold using tags.

Point

This line contains actual data samples. Here, "data" will contain these fields:

  • "time" - timestamp when the sample was collected
  • "value" - the actual data sample; time values are in milliseconds
  • "tags" - dictionary with tagname-tagvalue pairs that can be used when filtering results data

Processing JSON output

We recommend using jq to process the k6 JSON output. jq is a lightweight and flexible command-line JSON processor.

You can quickly create filters to return a particular metric of the JSON file:

jq '. | select(.type=="Point" and .metric == "http_req_duration" and .data.tags.status >= "200")' myscript-output.json

And calculate an aggregated value of any metric:

jq '. | select(.type=="Point" and .metric == "http_req_duration" and .data.tags.status >= "200") | .data.value' myscript-output.json | jq -s 'add/length'
jq '. | select(.type=="Point" and .metric == "http_req_duration" and .data.tags.status >= "200") | .data.value' myscript-output.json | jq -s min
jq '. | select(.type=="Point" and .metric == "http_req_duration" and .data.tags.status >= "200") | .data.value' myscript-output.json | jq -s max

For more advanced cases, check out the jq Manual