Explain the execution flow of generating an HTML dashboard report from a JTL results file?

During a non-GUI test run, JMeter writes sample results incrementally to a JTL file, in CSV or XML format depending on configuration, capturing each sample's timestamp, response time, response code, thread name, and other configured fields as the test progresses.

After the test completes, running JMeter with the report-generation flags, typically jmeter -g results.jtl -o /path/to/report/output, tells JMeter to read that saved JTL file and process it entirely offline, without needing the original test plan or a live connection to the system under test at all.

JMeter's reporting engine aggregates the raw per-sample data from the JTL file into the statistics the dashboard actually displays - response time percentiles, throughput over time, active threads over time, and error rate breakdowns - computing these summaries from the complete result set rather than the running averages a live listener might have shown during the test itself.

The output directory is populated with a set of static HTML, CSS, and JavaScript files, along with the underlying aggregated data they render, forming a self-contained dashboard that can be opened directly in a browser or hosted on a web server for sharing with stakeholders, without needing JMeter itself installed to actually view it.

Because this entire process runs against the saved JTL file independent of the original test run, the same result file can be used to regenerate the dashboard multiple times, or the same command can be pointed at JTL files merged from multiple distributed agents, letting a single consolidated report be produced from a distributed test's combined results after the fact.

flowchart LR
  A[Non-GUI test run] --> B[Samples written incrementally to JTL file]
  B --> C[Test completes]
  C --> D["jmeter -g results.jtl -o output/"]
  D --> E[Reporting engine aggregates JTL data offline]
  E --> F[Static HTML/CSS/JS dashboard generated]