plan

An architecture-planning workflow for a software feature after its acceptance criteria and specifications are prepared. It proposes how the code should be designed and asks the human to confirm the architectural direction.

In plain words
What is it for?
Use it to design a feature's architecture and produce its implementation plan after acceptance criteria and, ideally, a formal specification exist.
Why use it?
It provides an explicit design checkpoint before implementation, including review of code structure and performance choices. It also checks that earlier specification steps and branch conditions are complete.

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/swingerman/engineer/plan
Any agent
npx skills add swingerman/engineer --skill plan
Clone the repo
git clone --depth 1 https://github.com/swingerman/engineer

Made for: Claude Code, Codex.

Per session 42 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 2,381 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 $0.00042 $0.02381
Opus 5 $0.00021 $0.01190
Sonnet 5 $0.00008 $0.00476
Haiku 4.5 $0.00004 $0.00238

Measured 2d ago against content hash e8d15c2605d1, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

plan 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.

engineer/skills/plan/SKILL.md · 63 lines

How it starts

The opening of the file, as written. The whole thing — 63 lines — stays where its author put it; the contents beside it link to each section on GitHub.

plan

Produce a feature's architecture plan — Checkpoint 4, the most consequential architectural checkpoint. Where engineering authority over code design and performance is exercised: the agent proposes, the human decides.

Mixed mode — the agent proposes the architecture, the human confirms it, then the rest of the plan is drafted.

When to use

After discover-acs (Checkpoint 2) and atdd:atdd (Checkpoint 3). Produces plan.md.

If spec.md is missing, warn — planning should follow spec formalization — but the user may override and plan from acs.md alone (flag the skipped step in the handoff).

Not for: Given/When/Then specs (atdd:atdd); small changes to an existing plan (feature-edit).

Workflow

Step 0 — Entry gate. Before starting, verify the prior checkpoint is complete: run ${CLAUDE_PLUGIN_ROOT}/scripts/dae_handoff.py <feature-dir> --through 3. On a non-zero exit, stop and surface the gap to the human — do not proceed.

Verify branch hygiene: run ${CLAUDE_PLUGIN_ROOT}/scripts/dae_branch.py <feature-dir>. On a non-zero exit, stop and surface the message to the human — switch branches and re-invoke. The check honors the git.manual: true manifest opt-out.

After the gate passes, show the pipeline breadcrumb: run ${CLAUDE_PLUGIN_ROOT}/scripts/dae_progress.py <feature-dir> and present its output to the human — it shows where this checkpoint sits in the DAE pipeline. The breadcrumb is advisory: a non-zero exit or a missing progress.md never blocks the skill. Then create one TodoWrite todo per workflow step below. See ${CLAUDE_PLUGIN_ROOT}/references/progress-indicator.md.

  1. Resolve + load — resolve the methodology root + manifest via ${CLAUDE_PLUGIN_ROOT}/scripts/dae_resolve.py (see references/resolving.md); load feature.md, acs.md, spec.md, CHARTER.md.
  2. Propose the architecture — draft only the Architecture section (components, data flow, where new code lives, coupling, key decisions + rationale + alternatives). Pin cross-track interface contracts: for any interface shared across parallel implementation tracks (a client and a backend built concurrently, two services, etc.), specify the exact wire contract — field names, casing, JSON shape, status codes — not a prose sketch or ASCII diagram. A loose contract forces the other track to reverse-engineer and guess (wsapi /auth/firebase was left as {idToken} with no casing; the parallel client shipped a snake_case guess that had to be reconciled later). This is the interface-pinning that makes parallel tracks safe — see ${CLAUDE_PLUGIN_ROOT}/references/parallelism.md. Ground it in the actual code: prefer LSP — workspaceSymbol to locate the components you'll touch, call-hierarchy (incomingCalls/outgoingCalls) to map coupling and blast radius, findReferences before proposing a change to a shared symbol — over grep, when an LSP MCP capability is available; fall back to grep + Read otherwise (see ${CLAUDE_PLUGIN_ROOT}/references/code-lookup.md). Present it; iterate until the human confirms. Do not draft the rest until then. Gate-profile branch (see ${CLAUDE_PLUGIN_ROOT}/references/gate-profile.md): the mid-way "iterate until the human confirms" stop applies when the feature's gate_profile is absent, or when autonomy_level is low (low suppresses front-dialing — the human reviews everything). Under front: bundled or auto at medium/high, do not stop here — draft the architecture and the rest in one pass; the architecture is approved with the bundle at Step 6 (bundled) or trusted to the gauntlet + back gate (auto). Architecture stays a human decision under bundled; only when it's approved changes.
  3. Draft the rest — draft the remaining sections. When gate_profile is absent, the human confirms Step 2's architecture first, then reviews the finished file. Under bundled/auto, draft straight through. Let gate_profile.verify set the Test strategy's back-gate depth: heavy → an explicit human validation step named in validation_method; light → lean on the objective gates (acceptance + CRAP + mutation + gauntlet) and say so.
  4. Charter Check — validate the plan against CHARTER.md. Produce the two-part structured check: a compliance table (one row per charter rule, plus auto-rows for autonomy stance, verification independence, mutation policy, and — at high autonomy — performance budgets), and an Amendments section. Hard rule: never finish a plan with a ⚠️ deviation that lacks a matching amendment ADR. Either write the amendment inline, or stop and emit a handoff with human_action_needed: decision.
  5. Write plan.md — frontmatter (slug, checkpoint: 4, plan_status, created) + sections: Architecture, Charter Check, Phasing, Performance budgets, Collaboration schedule, Execution modes, Test strategy. Test strategy must explicitly incorporate feature.md's validation_method if it carries a non-default value — e.g. if validation_method is "canary 5% prod for 24h, watch dashboard X," the Test strategy section names the canary phase, the dashboard, and the rollback trigger. If validation_method is absent, default to the standard DAE stack (acceptance + unit + mutation per charter) and say so explicitly. Declare the gauntlet bar in Test strategy when the feature has something to build against that the tests can't assert — a design export, a reference UI screenshot or URL, a reference implementation, a golden output. Emit the gauntlet: block (bar paths + capture: command + max_rounds) per ${CLAUDE_PLUGIN_ROOT}/references/gauntlet.md; CP5 loops builder↔critic against it after green instead of handing the grading back to the human. No such reference exists → omit the block entirely; the absence is the opt-out and no gauntlet runs. A bar must be inspectable — never write prose ("matches the design system") or the ACs into it. A promoted prototype is the bar by default: if feature.md carries a prototype: path (from the prototype skill), declare that path as the gauntlet: bar automatically, with a capture: that renders/runs the candidate in the same form — the prototype is iteration 0's reference, no separate bar needed.
  6. Review panel — dispatch the standing adviser + advocate pair against plan.md per ${CLAUDE_PLUGIN_ROOT}/references/review-panel.md. This is the last gate before code exists, and a plan resting on a false premise is the most expensive thing to discover at CP5 — one ei-theme plan's central factual claim about a shared template turned out to be wrong, and only the advocate caught it. Give both briefs the source files the Architecture section makes claims about, not just the artifacts. Autonomy-keyed; skip silently when the plan is a one-module addition with no architectural argument. Fold the findings into plan.md, then record every finding — accepted or rejected — as panel_findings[] in the handoff. An unaddressed error-severity finding blocks the CP5 dispatch.
  7. Generate runbook.md if the plan touches infra/operator steps — provisioning (cloud project create, billing link, API enablement), secrets management, console-only configuration, manual DNS, deploy-day toggles. Use references/runbook-template.md. Each step has [ ] human or [ ] agent ownership, optional command: if runnable, and evidence: for completion. Deploy-related ACs (e.g. "site loads at staging URL") MUST NOT claim green until the runbook's prerequisite steps are checked off. If the plan has no infra/operator surface, skip — no empty file.
  8. Handoff — emit a summary.

Read the full file on GitHub · 63 lines

Files

What ships with it

1 file 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 · 63 lines · 42 tokens per session scan A e8d15c2605d1

Subscribe to this mod's changes

plan is a skill published in the GitHub repository swingerman/engineer (146 stars, last pushed 6d ago), licensed MIT. It adds 42 tokens to every session and 2,381 once invoked, about $0.0002 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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