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

JSON format

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

Summary export

If you don't care about each individual metric measurement and instead want to see only the aggregated data, exporting the end-of-test summary data to a JSON file might be a better choice than using the JSON output described here. For more details, see --export-summary and handleSummary() in the end-of-test summary docs.

See also

• Metrics