json-output.md

JSON output reference

Use --json or --output-format json to emit a single JSON document on stdout. Text progress and the human-readable summary are suppressed; stderr may still show progress unless --no-progress is set.

Top-level fields

Field	Type	Description
url	string	Target URL shown in the report (multi-URL runs use http://first (+N more))
duration_mode	boolean	true when the run used -d, otherwise request-count mode
summary	object	Throughput and error-rate summary
transfer	object	Response body size metrics
latency_ms	object	Latency aggregates in milliseconds
latency_histogram	array	Rolled-up histogram buckets
status	object	HTTP success/failure breakdown

summary

Field	Type	Description
requests	integer	Total attempts (responses + transport errors)
responses	integer	Completed HTTP responses
transport_errors	integer	Connection/TLS/IO failures
elapsed_seconds	number	Wall-clock benchmark duration
requests_per_second	number	requests / elapsed_seconds
failure_rate_percent	number	(failed HTTP + transport errors) / requests * 100

transfer

Field	Type	Description
total_bytes	integer	Sum of response body bytes
size_per_request_bytes	number	Average bytes per HTTP response
bytes_per_second	number	Throughput in bytes/sec

latency_ms

All values are in milliseconds.

Field	Description
avg, min, max, stdev	Basic latency stats
p10, p25, p50, p75, p90, p95, p99, p999	Percentiles

latency_histogram[]

Field	Type	Description
start_ms	number	Bucket start (inclusive)
end_ms	number	Bucket end
count	integer	Requests in bucket
percent	number	Share of total requests

status

Field	Type	Description
success_statuses	string[]	Configured success code ranges
successful_count	integer	Responses counted as success
successful_percent	number	Share of HTTP responses
failed_count	integer	HTTP responses outside success ranges
failed_percent	number	Share of HTTP responses
transport_error_percent	number	Share of all attempts
codes[]	array	{ "code", "count", "percent" } per HTTP status
transport_errors[]	array	{ "category", "count", "percent" } per error class

Example

cryload http://localhost:3000/api -n 500 --json > result.json
jq '.summary.requests, .latency_ms.p99, .status.successful_count' result.json

CI checks

cryload http://localhost:3000/api -n 1000 --json > result.json
jq -e '.summary.failure_rate_percent <= 1' result.json
jq -e '.latency_ms.p99 <= 250' result.json

See also README for a GitHub Actions workflow example.