capacity-planning

Capacity Planning Skill

Produce a complete capacity planning document for a service. Capacity planning is not about predicting the future exactly — it is about understanding current headroom, modelling growth, and ensuring the team takes infrastructure action before a constraint becomes an incident.

A good capacity plan answers: what is running out first, how long before it runs out, what does it cost to fix it, and who decides when to act.

Required Inputs

Ask for these if not already provided:

• Service name and description — what the service does and who depends on it
• Current traffic and usage metrics — requests per second (or per day), active users, data volume — whatever units are most natural for this service
• Current resource utilisation — CPU %, memory %, disk usage, connection pool utilisation, DB query throughput
• Growth rate or projections — historical growth rate, or known upcoming events (product launch, sales cycle, seasonal peak)
• Tech stack and infrastructure — cloud provider, compute type (VMs, containers, serverless), database, caching layer, CDN
• Cost constraints — current infrastructure spend, acceptable cost ceiling, or target cost per unit of traffic

Output Format

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Capacity Plan: [Service Name]

Service: [Name] | Team: [Team name] Author: [Name] | Last updated: [Date] Planning horizon: [12 months — [Month Year] to [Month Year]] Review cadence: [Quarterly]

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1. Executive Summary

[3–5 sentences covering: current state, the most critical capacity constraint, the timeline before it becomes a risk, the recommended action, and the cost implication. Written for an engineering manager or VP who needs the key facts without reading the full document.]

Critical finding: [e.g. "The database connection pool will reach 90% utilisation within 6 weeks at current growth. Without action, this will cause request queueing and latency spikes under normal traffic."]

Recommended immediate action: [e.g. "Increase connection pool limit and add a read replica within the next 2 weeks."]