dotnet-mcaf-feature-spec

A guide for writing a feature specification: a document that describes the intended behavior of a software change. It records business rules, user journeys, system behavior, checks, and the Definition of Done, meaning the conditions for considering the work complete.

In plain words
What is it for?
Use it for substantial behavior changes, acceptance criteria, executable requirements, user-flow documentation, and edge-case definitions. It is not intended for cosmetic changes or small typo fixes.
Why use it?
Vague requirements make engineers guess and make tests disagree about expected behavior. This creates a shared reference before or during implementation.

Skill for Claude CodeCodex

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/managedcode/prompterone/dotnet-mcaf-feature-spec
Any agent
npx skills add managedcode/PrompterOne --skill dotnet-mcaf-feature-spec
Clone the repo
git clone --depth 1 https://github.com/managedcode/PrompterOne

Made for: Claude Code, Codex.

Per session 76 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 860 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 $0.00076 $0.00860
Opus 5 $0.00038 $0.00430
Sonnet 5 $0.00015 $0.00172
Haiku 4.5 $0.00008 $0.00086

Measured 2d ago against content hash b78a2b9aea60, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

dotnet-mcaf-feature-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 2d 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.

Origin

Copies of this mod

3 near-identical copies found in the catalogue:

.codex/skills/dotnet-mcaf-feature-spec/SKILL.md · 103 lines

How it starts

The opening of the file, as written. The whole thing — 103 lines — stays where its author put it; the contents beside it link to each section on GitHub.

MCAF: Feature Spec

Trigger On

  • add or change non-trivial behaviour
  • behaviour is under-specified and engineers are guessing
  • tests need a stable behavioural source of truth

Value

  • produce a concrete project delta: code, docs, config, tests, CI, or review artifact
  • reduce ambiguity through explicit planning, verification, and final validation skills
  • leave reusable project context so future tasks are faster and safer

Do Not Use For

  • architecture decisions that need alternatives and trade-offs
  • tiny typo or cosmetic-only changes with no behavioural impact

Inputs

  • docs/Architecture.md
  • the nearest AGENTS.md
  • current user flows, business rules, and acceptance expectations

Quick Start

  1. Read the nearest AGENTS.md and confirm scope and constraints.
  2. Run this skill's Workflow through the Ralph Loop until outcomes are acceptable.
  3. Return the Required Result Format with concrete artifacts and verification evidence.

Workflow

  1. Define scope first: in scope, out of scope, boundaries touched.
  2. If the feature doc is missing, scaffold from references/feature-template.md.
  3. Keep the spec executable:
    • numbered rules
    • main flow
    • edge and failure flows
    • system behaviour
    • verification steps
    • Definition of Done
  4. Make the spec concrete enough that tests can be written without guessing.
  5. If the feature creates a new dependency, boundary, or major policy shift, update an ADR too.

Deliver

  • docs/Features/feature-name.md
  • a feature spec that engineers and agents can implement directly

Validate

  • rules are testable, not aspirational
  • edge cases are captured where they matter
  • verification steps match the intended behaviour
  • the doc can drive implementation without hidden tribal knowledge

Ralph Loop

Use the Ralph Loop for every task, including docs, architecture, testing, and tooling work.

  1. Brainstorm first (mandatory):
    • analyze current state
    • define the problem, target outcome, constraints, and risks
    • generate options and think through trade-offs before committing
    • capture the recommended direction and open questions
  2. Plan second (mandatory):
    • write a detailed execution plan from the chosen direction
    • list final validation skills to run at the end, with order and reason
  3. Execute one planned step and produce a concrete delta.
  4. Review the result and capture findings with actionable next fixes.
  5. Apply fixes in small batches and rerun the relevant checks or review steps.
  6. Update the plan after each iteration.
  7. Repeat until outcomes are acceptable or only explicit exceptions remain.
  8. If a dependency is missing, bootstrap it or return status: not_applicable with explicit reason and fallback path.

Read the full file on GitHub · 103 lines

Files

What ships with it

2 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. 2d ago First seen · 103 lines · 76 tokens per session scan A b78a2b9aea60

Subscribe to this mod's changes

dotnet-mcaf-feature-spec is a skill published in the GitHub repository managedcode/PrompterOne (42 stars, last pushed 3mo ago), licensed MIT. It adds 76 tokens to every session and 860 once invoked, about $0.0004 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 2026-08-30.

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