Real-Time Result Streaming

Besides the end-of-test summary, k6 can stream metrics as granular data points in real time. This enables live monitoring, long-term storage, and integration with external observability platforms.

Overview

Real-time streaming allows you to:

Monitor test progress as it runs
Store metrics for historical analysis
Integrate with existing monitoring systems
Build custom dashboards and alerts
Process metrics with your own tools

You can stream metrics to either files or external services using the --out flag.

Output to Files

k6 supports streaming metrics to local files in two formats:

CSV

Simple, human-readable format

k6 run --out csv=results.csv script.js

JSON

Structured format with full metadata

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

CSV Output

CSV output provides a simple, tabular format with one metric value per line:

k6 run --out csv=test_results.csv script.js

You can also compress the output automatically:

k6 run --out csv=test_results.gz script.js

CSV Format:

metric_name,timestamp,metric_value,check,error,error_code,group,method,name,proto,scenario,status,subproto,tls_version,url,extra_tags
http_reqs,1595325560,1.000000,,,,,GET,http://test.k6.io,HTTP/1.1,default,200,,,http://test.k6.io,
http_req_duration,1595325560,221.899000,,,,,GET,http://test.k6.io,HTTP/1.1,default,200,,,http://test.k6.io,
http_req_blocked,1595325560,225.275000,,,,,GET,http://test.k6.io,HTTP/1.1,default,200,,,http://test.k6.io,
http_req_connecting,1595325560,217.680000,,,,,GET,http://test.k6.io,HTTP/1.1,default,200,,,http://test.k6.io,
vus,1595325560,1.000000,,,,,,,,,,,,,
vus_max,1595325560,20.000000,,,,,,,,,,,,,
checks,1595325561,1.000000,status is 200,,,,,,,default,,,,,
data_sent,1595325561,76.000000,,,,,,,,default,,,,,
data_received,1595325561,11045.000000,,,,,,,,default,,,,,
iteration_duration,1595325561,1449.049580,,,,,,,,default,,,,,
iterations,1595325561,1.000000,,,,,,,,default,,,,,

CSV Configuration:

Option	Environment Variable	Description	Default
`saveInterval`	`K6_CSV_SAVE_INTERVAL`	How often to flush data	`1s`
`timeFormat`	`K6_CSV_TIME_FORMAT`	Timestamp format: `unix`, `unix_nano`, `unix_micro`, `unix_milli`, `rfc3339`, `rfc3339_nano`	`unix`
`fileName`	`K6_CSV_FILENAME`	Output file path	`file.csv`

Monitor in real time:

# In terminal 1
k6 run --out csv=results.csv script.js

# In terminal 2
tail -f results.csv

JSON Output

JSON output provides structured data with complete metric metadata:

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

Or compressed:

k6 run --out json=test_results.gz script.js

JSON Format: Each line contains either a metric definition or a data point:

{"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<1000"],"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://test.k6.io/api/tools"}},"metric":"http_req_duration"}

Process with jq:

# Filter specific metrics
jq '. | select(.type=="Point" and .metric == "http_req_duration" and .data.tags.status >= "200")' results.json

# Calculate average
jq '. | select(.type=="Point" and .metric == "http_req_duration") | .data.value' results.json | jq -s 'add/length'

# Find min/max
jq '. | select(.type=="Point" and .metric == "http_req_duration") | .data.value' results.json | jq -s min
jq '. | select(.type=="Point" and .metric == "http_req_duration") | .data.value' results.json | jq -s max

For the aggregated end-of-test summary as JSON, use the handleSummary() function instead of --out json.

Output to Services

k6 can stream metrics to various external services and databases:

Grafana Cloud
InfluxDB
Prometheus
Other Services

Stream directly to Grafana Cloud k6 for managed storage and visualization:

k6 run --out cloud script.js

Requires a Grafana Cloud k6 account.

InfluxDB v1 (built-in support):

k6 run --out influxdb=http://localhost:8086/myk6db script.js

InfluxDB v2 (requires extension):

# Build custom k6 with extension
xk6 build --with github.com/grafana/xk6-output-influxdb

# Run with configuration
K6_INFLUXDB_ORGANIZATION="my-org" \
K6_INFLUXDB_BUCKET="k6-results" \
K6_INFLUXDB_TOKEN="my-token" \
K6_INFLUXDB_ADDR="http://localhost:8086" \
./k6 run -o xk6-influxdb script.js

Stream to Prometheus using remote write:

k6 run --out experimental-prometheus-rw script.js

Configure with environment variables:

K6_PROMETHEUS_RW_SERVER_URL=http://localhost:9090/api/v1/write \
K6_PROMETHEUS_RW_TREND_AS_NATIVE_HISTOGRAM=true \
k6 run --out experimental-prometheus-rw script.js

InfluxDB Example

Here’s a complete workflow for streaming to InfluxDB v2:

Install xk6

go install go.k6.io/xk6/cmd/xk6@latest

Build k6 with extension

xk6 build --with github.com/grafana/xk6-output-influxdb

Run test

K6_INFLUXDB_ORGANIZATION="my-org" \
K6_INFLUXDB_BUCKET="k6-results" \
K6_INFLUXDB_TOKEN="my-token" \
K6_INFLUXDB_ADDR="http://localhost:8086" \
./k6 run -o xk6-influxdb script.js

Visualize in Grafana

Connect Grafana to your InfluxDB instance and use pre-built dashboards or create custom ones.

InfluxDB v2 Configuration Options:

Environment Variable	Default	Description
`K6_INFLUXDB_ORGANIZATION`	-	InfluxDB organization name
`K6_INFLUXDB_BUCKET`	-	Bucket name for k6 metrics
`K6_INFLUXDB_TOKEN`	-	API token for authentication
`K6_INFLUXDB_ADDR`	`http://localhost:8086`	InfluxDB server address
`K6_INFLUXDB_PUSH_INTERVAL`	`1s`	Metric flush frequency
`K6_INFLUXDB_CONCURRENT_WRITES`	`4`	Number of concurrent write requests
`K6_INFLUXDB_TAGS_AS_FIELDS`	`vu:int,iter:int,url`	Comma-separated tags to store as fields
`K6_INFLUXDB_INSECURE`	`false`	Skip HTTPS certificate verification

Multiple Outputs

You can stream to multiple destinations simultaneously:

k6 run \
  --out json=results.json \
  --out influxdb=http://localhost:8086/k6db \
  --out csv=results.csv \
  script.js

This is useful for:

Archiving raw data while monitoring in real time
Sending to multiple monitoring systems
Creating backups of test results

Docker Example

Stream results when running k6 in Docker:

docker run -it --rm \
  -v $(pwd):/scripts \
  -v $(pwd)/results:/output \
  grafana/k6 run \
  --out json=/output/results.json \
  /scripts/script.js

Ensure the Docker user has write permissions to the output directory.

Performance Considerations

Streaming real-time metrics can impact test performance, especially at high load. Consider:

Increasing saveInterval or pushInterval for high-throughput tests
Using efficient backends (InfluxDB, Prometheus) instead of JSON files
Running k6 and the monitoring backend on separate machines
Monitoring the resource usage of both k6 and the output backend

Building Custom Output Extensions

You can create your own output format using xk6:

package myoutput

import (
    "go.k6.io/k6/output"
)

func init() {
    output.RegisterExtension("myoutput", New)
}

func New(params output.Params) (output.Output, error) {
    // Your implementation
}

For details, see the output extension documentation.

Next Steps

Grafana Dashboards

Visualize real-time metrics with Grafana

Web Dashboard

Use the built-in web dashboard for live monitoring

Metrics Reference

Learn about all available k6 metrics

Output Extensions

Build custom output formats

Using k6

Testing Guides

Browser Testing

Results & Visualization

Real-Time Result Streaming

Real-Time Result Streaming

Overview

Output to Files

CSV

JSON

CSV Output

JSON Output

Output to Services

InfluxDB Example

Multiple Outputs

Docker Example

Performance Considerations

Building Custom Output Extensions

Next Steps

Grafana Dashboards

Web Dashboard

Metrics Reference

Output Extensions

Build docs developers (and LLMs) love

Using k6

Testing Guides

Browser Testing

Results & Visualization

​Real-Time Result Streaming

​Overview

​Output to Files

CSV

JSON

​CSV Output

​JSON Output

​Output to Services

​InfluxDB Example

​Multiple Outputs

​Docker Example

​Performance Considerations

​Building Custom Output Extensions

​Next Steps

Grafana Dashboards

Web Dashboard

Metrics Reference

Output Extensions

Build docs developers (and LLMs) love

Real-Time Result Streaming

Overview

Output to Files

CSV Output

JSON Output

Output to Services

InfluxDB Example

Multiple Outputs

Docker Example

Performance Considerations

Building Custom Output Extensions

Next Steps