NFR Architect

Overview

NFR Architect guides teams through the full lifecycle of non-functional requirements: writing well-formed NFRs that satisfy the BINT criteria, translating them into SLOs and SLIs, and producing concrete fitness functions that turn requirements into executable tests.

Reference file references/nfr-guide.md for full definitions, translation patterns, template code, and common pitfalls. Load it into context at the start of any session.

Workflow

Step 1 — Elicit and Validate NFRs (BINT Check)

When a user presents or describes an NFR, evaluate it against all four BINT criteria:

Bounded — Is it scoped to a specific service, time window, and load condition?
Independent — Does it stand alone without depending on another NFR?
Negotiable — Is there an explicit business driver (KPI, SLA, risk) behind it?
Testable — Does it have a quantified, automatable acceptance criterion?

If any criterion fails, rewrite the NFR using the anatomy pattern from the reference:

[Subject] shall [metric verb] [quantified threshold]
  [during/within] [bounded context / time window]
  [under] [defined load or condition]

Ask clarifying questions to fill any gaps:

What service or component does this apply to?
What is the load condition or time window?
What business outcome breaks if this is violated?
What is the measurement source (logs, APM, synthetic probe)?

Step 2 — Translate NFR → SLO + SLI

Once an NFR is valid, produce the corresponding SLO and SLI using the patterns in references/nfr-guide.md (Performance, Availability, Resilience, Security / Structural).

For each NFR, output a table:

| Element | Value | |---------|-------| | NFR | Original statement | | SLO | Internal target (stricter than SLA) | | SLI formula | (good events / total events) × 100 or equivalent | | Measurement source | Tool, query, or probe | | Error budget | 1 − SLO headroom | | Measurement window | Rolling 30-day / per-incident / etc. |

SLOs must always be equal to or stricter than the corresponding SLA. Flag any violation.

Step 3 — Generate Fitness Functions

Produce automatable fitness function code that enforces the SLO.

Choose the right tool based on NFR category:

| Category | Recommended Tools | |----------|------------------| | Performance (latency/throughput) | k6, Gatling, Locust, JMeter | | Availability | Synthetic probes, Datadog monitors, Pingdom | | Architecture / structural | ArchUnit (Java), Dependency Cruiser (JS/TS), py-arch-rule (Python) | | Resilience / recovery | Chaos engineering scripts, DR drill harnesses | | Security | Snyk in CI, OWASP ZAP, Trivy |

For each fitness function, specify:

File path — e.g., fitness-function/performance/checkout-slo.js
CI stage — where it runs (PR check, nightly, quarterly drill)
Failure action — block deploy, alert on-call, fail PR
Threshold values — wired directly from the SLO

Use the code templates in references/nfr-guide.md as starting points. Always wire thresholds from the SLO statement — never use placeholder values.

Step 4 — Produce the NFR Document

Use the NFR Documentation Template from references/nfr-guide.md to produce a complete, structured NFR record per requirement. Include:

NFR statement
Bounded context
Acceptance criteria checklist
SLO table
SLI formula and measurement source
Fitness function file reference
Trade-off notes tied to the business driver

Core Rules

Never accept an unbounded NFR (e.g., "shall be fast"). Always quantify.
SLOs must be stricter than (or equal to) any corresponding SLA.
Every NFR must have at least one fitness function. "Testable" is the most important BINT criterion.
Fitness function thresholds must be derived from SLO values — no hardcoded magic numbers.
Architecture NFRs (dependency constraints, layering rules) must produce ArchUnit / Dependency Cruiser tests committed to the codebase and run in CI.

Quick Reference

| Term | One-line definition | |------|---------------------| | NFR | How well the system performs a quality attribute | | BINT | Bounded, Independent, Negotiable, Testable | | SLO | Internal measurable target, stricter than SLA | | SLI | Actual measured value tracked against SLO | | Error budget | Allowable failure headroom = 1 − SLO | | Fitness function | Automated test that enforces an NFR/SLO |

For full examples, translation patterns, code templates, and common pitfalls, read references/nfr-guide.md.