nfr-spec

nfr-spec is a skill for Claude Code from sananthanarayan/skilldrop. It costs 104 tokens per session (1,526 once invoked), scanned A, original, MIT.

A checklist for defining non-functional requirements: how well a system must perform, remain available, protect data, support users, and operate in production.

In plain words
What is it for?
Use it after describing a feature to set measurable requirements for latency, capacity, uptime, backups, privacy, accessibility, languages, monitoring, compatibility, and cost. These requirements can guide architecture and testing.
Why use it?
It prevents important quality expectations from being left unspecified by requiring each category to have a target, an explicit exclusion, or a marked assumption.

Skill for Claude Code

Written for Claude Code: shipped in a Claude Code plugin.

Part of the skilldrop plugin — 51 skills, 4 agents shipped together

Install

Getting it into your agent

One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.

agentmods
npx agentmods add skills/sananthanarayan/skilldrop/nfr-spec
Any agent
npx skills add sananthanarayan/skilldrop --skill nfr-spec
Clone the repo
git clone --depth 1 https://github.com/sananthanarayan/skilldrop

Made for: Claude Code.

Or install skilldrop, the plugin that ships this one along with the rest of its 51 skills, 4 agents.

Wrote this? Show the measurements

A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.

agentmods badge for nfr-spec

README.md
[![agentmods](https://agentmods.dev/badge/skills/sananthanarayan/skilldrop/nfr-spec.svg)](https://agentmods.dev/skills/sananthanarayan/skilldrop/nfr-spec)
Your own site
<a href="https://agentmods.dev/skills/sananthanarayan/skilldrop/nfr-spec"><img src="https://agentmods.dev/badge/skills/sananthanarayan/skilldrop/nfr-spec.svg" alt="Measured on agentmods" height="20"></a>
Per session 104 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 1,526 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. Scan, not verified.
Origin original No closer match found in the catalogue.
Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

ModelPer sessionOnce invoked
Fable 5.1 $0.00104 $0.01526
Opus 5 $0.00052 $0.00763
Sonnet 5 $0.00021 $0.00305
Haiku 4.5 $0.00010 $0.00153

Measured 6d ago against content hash 6e952b1fc66e, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-06, from the pricing page.

Security

Grade A, and why

nfr-spec scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 6d ago.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Nothing flagged

None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.

skills/nfr-spec/SKILL.md · 64 lines

How it starts

The opening of the file, as written. The whole thing — 64 lines — stays where its author put it; the contents beside it link to each section on GitHub.

nfr-spec

Gathers the requirements nobody volunteers: the business says what the feature does, this skill pins down how well — with numbers. Every category in the catalog ends in exactly one of three states: a measurable target with a verification method, an explicit n/a with a reason, or an accepted default tagged [assumption]. Silence is the one forbidden state. Downstream of prd-draft; feeds design-doc (targets shape the architecture), test-plan-generator (verification methods become test cases), and threat-model (security depth lives there, not here).

How to respond

  1. Classify the system first — the archetype sets the defaults: customer-facing SaaS, internal tool, public API, batch/pipeline, mobile/edge. Ask at most 2 questions, spent on the two answers that move the most targets: user-facing or internal, and what happens when it's down for an hour (the honest availability requirement hides in that answer). Everything else: archetype default + [assumption].

  2. Sweep every category in reference.md — performance/latency, throughput/capacity, availability/SLO, durability/backup/DR, privacy/retention/residency, accessibility, i18n/l10n, observability, operability, compatibility, cost. For each: target, verification, or n/a-with-reason. The output includes the full ledger so a reviewer sees the sweep happened — a skipped category is indistinguishable from a forgotten one otherwise.

  3. Force numbers tied to business reality, not aspiration."p95 search < 800ms at 2× current peak (peak = 120 rps [data: April dashboard])" — ❌ "sub-second response times" (which percentile? at what load?) — ❌ "99.999% availability" for an internal tool whose users sleep at night (five nines costs 100× three nines; the archetype default exists to stop this).

  4. Attach a verification method to every target — the method that would prove it before launch, not after: load test at stated volume, chaos drill, restore-from-backup rehearsal, axe-core scan + screen-reader pass, locale pseudo-translation run, cost projection at target volume. An NFR without a verification is a hope with units. These methods hand straight to test-plan-generator.

Read the full file on GitHub · 64 lines

Files

What ships with it

5 files beside SKILL.md in the same directory: the scripts, references and assets a skill reads on demand. Not counted in the per-session cost; read them before you install if any of them is executable.

Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

  1. 6d ago First seen · 64 lines · 104 tokens per session scan A 6e952b1fc66e

Subscribe to this mod's changes

nfr-spec is a skill published in the GitHub repository sananthanarayan/skilldrop (2 stars, last pushed 22d ago), licensed MIT. It adds 104 tokens to every session and 1,526 once invoked, about $0.0005 per session on Opus 5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-31.

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