bdd

A way to develop software by first describing the behavior people need in concrete examples, then turning those examples into automated tests. BDD stands for behavior-driven development, and Gherkin is a plain-text format using Given, When, and Then steps.

In plain words
What is it for?
It helps explore a feature or bug, write behavior scenarios, and implement them through the red-green-refactor testing cycle.
Why use it?
It reduces misunderstandings by making expected behavior clear before implementation and gives developers tests that show whether the behavior works.

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/fradser/dotclaude/bdd
Any agent
npx skills add FradSer/dotclaude --skill bdd
Clone the repo
git clone --depth 1 https://github.com/FradSer/dotclaude

Made for: Claude Code, Codex.

Per session 60 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 1,647 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 $0.00060 $0.01647
Opus 5 $0.00030 $0.00823
Sonnet 5 $0.00012 $0.00329
Haiku 4.5 $0.00006 $0.00165

Measured 2d ago against content hash f7be22f353e1, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

bdd 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.

mattpocock/skills/engineering/bdd/SKILL.md · 106 lines

How it starts

The opening of the file, as written. The whole thing — 106 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Behavior-Driven Development (BDD)

BDD is not just about tools; it's a methodology for shared understanding and high-quality implementation. This skill governs the Discovery → Formulation → Automation lifecycle: Gherkin scenarios define the behavior, and the Automation phase (red-green loop) is delegated to /mattpocock:tdd (BDD-driven).

When exploring the codebase, read CONTEXT.md (if it exists) so test names and interface vocabulary match the project's domain language, and respect ADRs in the area you're touching.

How to Use This Skill

When the user asks for a feature, bug fix, or refactor, apply the following mindset:

  1. Understand Behavior First: Do not start coding until you know what the system should do.
  2. Define Scenarios: Create or ask for concrete examples (Gherkin) of the expected behavior.
  3. Drive Implementation with Tests: Use the Red-Green-Refactor cycle.

The BDD Cycle

The process flows from requirements to code:

  • Discovery: Clarify requirements through examples (The "Three Amigos").
  • Formulation: Write these examples as specific scenarios (Given/When/Then).
  • Automation: Implement using the red-green-refactor cycle via /mattpocock:tdd, which governs test quality, seams, mocking, and anti-patterns.

See ./references/bdd-best-practices.md for a detailed guide.

Writing Scenarios (Gherkin)

Scenarios are your "Executable Specifications".

  • Keep them declarative (business focus).
  • Avoid technical jargon and UI details.
  • One behavior per scenario.
  • Store executable scenarios in .feature files or the framework-native executable test format — not as code comments. Once implementation begins, translate the scenarios that will be automated into .feature files or the framework-native executable test format, so they double as living documentation.

See ./references/gherkin-guide.md for syntax and storage structure.

Automation Phase

The Automation phase (red-green loop) is governed by the /mattpocock:tdd skill (BDD-driven). When the Gherkin scenario is defined and the seam is agreed, invoke /mattpocock:tdd for:

Read the full file on GitHub · 106 lines

Files

What ships with it

6 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 · 106 lines · 60 tokens per session scan A f7be22f353e1

Subscribe to this mod's changes

bdd is a skill published in the GitHub repository FradSer/dotclaude (588 stars, last pushed 21d ago), licensed MIT. It adds 60 tokens to every session and 1,647 once invoked, about $0.0003 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.

Related

Other skills, from other repositories

systematic-debugging

Use when encountering any bug, test failure, or unexpected behavior, before proposing fixes.

obra/superpowers · 21 tokens

brainstorming

You MUST use this before any creative work - creating features, building components, adding functionality, or modifying behavior. Explores user intent, requirements and design before implementation.

obra/superpowers · 37 tokens

chat-pet-sprite-creation

Use when creating or changing VS Code chat pet sprite art, sprite sheets, state animations, eye treatments, Stable/Insiders variants, or pet transitions under src/vs/workbench/contrib/chat/browser/widget/media/chatPet.

microsoft/vscode · 53 tokens

cpu-profile-analysis

Analyze V8/Chrome CPU profiles (.cpuprofile) and DevTools trace files (Trace-.json). Use when: profiling performance, investigating slow functions, comparing code paths, finding bottlenecks, analyzing timeToRequest, understanding call trees from sampling profiler data, analyzing layout/paint/rendering, investigating…

microsoft/vscode · 71 tokens

agent-host-chat-contributions

Build and review cross-cutting agent-host chat behavior through lifecycle contributions. Use when adding turn lifecycle side effects, prompt or context injection, restored-history transformation, protocol-action observation, or when reviewing changes that add code to AgentSideEffects or AgentService.

microsoft/vscode · 56 tokens

auto-perf-optimize

Run agent-driven VS Code performance or memory investigations. Use when asked to launch Code OSS, automate a VS Code scenario, run the Chat memory smoke runner, capture renderer heap snapshots, take workflow screenshots, compare run summaries, or drive a repeatable scenario before heap-snapshot analysis.

microsoft/vscode · 62 tokens