Performance investigation
Skill RobinGru/AgentSkillForge/skills/performance-investigation
Portable, reusable instruction packages for AI coding assistants.
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Investigate a measured performance concern with a comparable baseline, bounded hypotheses, discriminating experiments, and proportionate regression protection. Use for observed latency, responsiveness, throughput, memory, or resource problems.
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SKILL.md
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Performance investigation
Treat performance work as an investigation, not a list of optimizations. Change behavior only after measurements identify a plausible bottleneck and an experiment can distinguish it from competing explanations.
Use this skill when
- A user reports a repeatable slow path, monitoring detects a regression, or a service-level objective or agreed budget is breached.
- A planned load change, resource limit, or measured responsiveness issue needs a risk assessment.
- A profiling artifact, trace, metric, or reproducible workload can guide an investigation.
Do not use this skill when
- Someone requests that code be faster but supplies no signal, affected journey, or target. Request those details and prepare a measurement plan instead.
- An asset, query, cache, or framework change is proposed without a measurement showing that it affects a measured problem.
- A structural refactor is the primary task. Use this skill only if measurement establishes a performance cause that the refactor must address.
Workflow
1. Signal
Record the observed issue and its impact: affected journey or operation, users or systems affected, frequency, onset, and reason it matters. Classify the signal as user report, alert, regression, budget breach, reproducible slow journey, resource exhaustion, or planned demand. Do not infer a cause from the symptom.
2. Baseline
Make measurements comparable. Record environment, build or revision, dataset, load shape, tool, sampling method and count, primary metric, side metrics, and known limits. State whether each result is lab data, field data, or both; do not combine them as though they had identical conditions. Preserve enough raw output or an accessible summary for another investigator to repeat the comparison.
3. Partition
Divide the affected path into observable portions before proposing a fix. Check only portions relevant to the signal, such as network transfer, server time, queueing, database or storage, serialization, cache behavior, client main thread, rendering, assets, concurrency, or memory collection. Record unknown portions explicitly.
Use web signals or backend signals when their scope matches the path.
4. Experiment
For each live hypothesis, use experiment design. Change one material variable, choose the smallest test that would produce a different result if the hypothesis were false, and keep comparable conditions. Do not rewrite a suspected N+1 query, render path, or cache layer before a measurement can distinguish it from alternatives.
5. Decide and guard
Retain, revert, or continue investigating based on observed results, not expectation. Any retained performance change needs before-and-after measurements for the primary metric plus relevant side effects. Choose proportionate protection: regression test, repository budget, telemetry, alert, load test, or documented manual check. Example budgets help format local targets; product and repository budgets take precedence.
Output contract
Report Signal, Baseline, Partition, Hypotheses, Experiments,
Decision, Before and after, Guard, and Limits. For every experiment
include:
- hypothesis and its supporting facts;
- smallest discriminating experiment;
- expected and actual result;
- decision and next information needed, if inconclusive.
Label claims as measured, observed, inferred, or unknown. State measurement limitations and unverified assumptions. Do not claim improvement without a comparable before-and-after result.
Investigation examples
See investigation examples for small API queueing, Vue input lag, and batch memory-spike investigations. They model questions and experiments, not universal implementation advice.