promql-cli — Prometheus Query CLI Skill

promql-cli (github.com/nalbury/promql-cli) is a Go CLI for querying, analyzing, and visualizing Prometheus metrics, plus PromQL fundamentals.

Reference Files

Read the relevant reference file(s) before executing tasks:

For most tasks, read references/usage.md. For PromQL help, read references/promql-reference.md. When debugging, read both references/debugging.md and references/promql-reference.md.

Setup Check

Before running any query, verify that a host is configured:

promql 'up'   # succeeds if host is reachable; fails with connection error if not configured
# or
promql --host xxx 'up'

Recognize these errors as a configuration/auth problem and refer to references/installation.md:

If any of these appear, do not create config files on behalf of the user — config files may contain credentials (tokens, passwords) that must never pass through an LLM. Instead, guide the user to set it up themselves:

"Please create ~/.promql-cli.yaml manually with your Prometheus host (and credentials if needed). See references/installation.md for the exact format. Let me know once it's ready."

Only after the user confirms the config is in place should you proceed with queries.

Quick Command Reference

promql 'up'                                          # instant query
promql 'rate(http_requests_total[5m])' --start 1h    # range query (ASCII graph)
promql 'up' --output csv                             # CSV output
promql 'up' --output json                            # JSON output
promql metrics                                       # list all metric names
promql labels <metric>                               # list labels for a metric
promql meta <metric>                                 # show metric type and help
promql --config ~/.promql-cli-prod.yaml 'up'         # target a specific host

Key Principles

1. Use rate() on counters, never raw values — raw counters only ever increase; the absolute value is meaningless. rate() gives the per-second change rate, which is what you actually care about.
2. When debugging, isolate a single instance — aggregating across replicas masks per-instance anomalies. A single overloaded pod hidden behind healthy peers won't show up in averages.
3. Filter early with label matchers in the innermost selector — Prometheus evaluates selectors before functions, so filtering late means scanning all time series. Early filters reduce data scanned and query latency.
4. For histograms, keep le in the by clause before histogram_quantile() — the function needs all le buckets to interpolate percentiles; dropping le early produces NaN or wrong results.
5. Prefer --output graph for range queries — ASCII sparklines convey trend direction (rising, falling, spiking) in a compact format that LLMs parse well; raw timestamp tables require mental modeling.
6. Store credentials in ~/.promql-cli.yaml and ~/.promql_token, chmod 600 — passing tokens as CLI args exposes them in shell history and process listings.

This skill is not exhaustive. Please refer to the official promql-cli documentation and examples for up-to-date information. Context7 can help as a discoverability platform.

If you encounter a bug or unexpected behavior in promql-cli itself, open an issue at https://github.com/nalbury/promql-cli/issues.