Turn "As Fast As Possible" Into a Spec

"As fast as possible." "Secure." "Reliable." Non-functional requirements often slip through the requirements phase written exactly like this — as vague adjectives instead of numbers. When a feature ships and turns out slower than expected, or a security gap surfaces, the root cause usually isn't a coding mistake. It's that no one wrote down a measurable threshold when the requirement was defined.

Why non-functional requirements surface late

Functional requirements are binary: a login flow either works or it doesn't. Non-functional requirements aren't — "how fast" and "how available" only become testable once someone attaches a number. Without one, the requirement passes review, passes QA, and lands in production where it finally collides with what a user or stakeholder expected. That collision gets reported as a bug, but it was a requirements gap from the start.

A number-first template for four categories

Split non-functional requirements into four categories — performance, availability, security, and operability — and write a number for each. Here's the before/after.

Performance

• Vague: "Pages should load reasonably fast."
• Numbered: "p95 LCP on core screens under 2.5s. API response time p95 under 300ms, p99 under 800ms."

Availability

• Vague: "The service should run reliably."
• Numbered: "99.9% monthly uptime (≈43 min allowed downtime/month). RTO 30 minutes, RPO 5 minutes."

Security

• Vague: "There should be no security issues."
• Numbered: "Auth tokens expire in 1 hour, refresh tokens in 30 days. OWASP Top 10 checked via static analysis before every release; zero High-severity findings allowed."

Operability

• Vague: "The system should be easy to operate."
• Numbered: "Error logs retained 90 days. Slack alert fires immediately if 5xx errors exceed 10 in 5 minutes. Dashboard lag under 1 minute."

Three questions every number needs

A number alone doesn't make a requirement enforceable. Pair each one with:

1. Who measures it — name the owner (e.g. the SRE team tracks p95 latency on a monitoring dashboard)
2. When it's measured — pre-release load testing, continuous production monitoring, or both
3. What happens if it's missed — agree in advance whether a missed threshold blocks release or gets logged as a known issue for the next sprint

Skip these three and the number becomes decorative — nobody is actually measuring against it, and you're back to discovering the gap after launch.

A common failure mode

The most common mistake isn't skipping numbers — it's picking numbers that don't match the project's stage. Bolting an enterprise-grade 99.99% uptime SLA onto an early MVP inflates cost and slows shipping for no real benefit. The opposite mistake — loose security thresholds on a feature touching payments or personal data — leads to serious incidents later. Calibrate each threshold to the actual risk and cost of the feature, rather than copy-pasting a template.

A checklist for requirements review

• Does every one of the four categories (performance, availability, security, operability) have a number?
• Are vague qualifiers like "reasonably" or "as much as possible" fully gone?
• Does each number have a named owner and a measurement method?
• Is the go/no-go rule for a missed threshold agreed upon in advance?
• Does the threshold's strictness match the feature's actual risk?

Bugoon in practice

Writing numbered non-functional requirements is only half the job — catching it when reality falls short of the number is the other half. Bugoon embeds as a lightweight widget, letting QA and non-engineers report bugs directly from the browser with a screenshot and automatically captured interaction steps. Reports about things like "this feels slow" or "this felt unstable" — the exact kind of non-functional complaints that are hard to pin down — come with reproduction steps attached and flow straight into a linked GitHub Issue, tracked on a kanban board. An MCP server for Claude Code and Cursor is also available, so an AI agent can work from that same report context when fixing the issue.