Imported from emiliosheinz/agent-skills (forge/SKILL.md). Install upstream with npx skills add emiliosheinz/agent-skills --skill forge. Copyright stays with the author.

Forge

Forge runs spec-driven development as four phases. You invoke one phase at a time. Each phase does its work, updates shared state, and recommends (but does not run) the next phase. A fifth command, fix, re-enters the flow to correct course at any layer. Every phase's depth auto-sizes to the change — see Sizing.

/forge specify <name>   Understand the problem + capture requirements   → spec.md
/forge design           Architecture, contracts, verification gates     → design.md
/forge plan             Atomic tasks, dependencies, AC traces            → plan.md
/forge execute          Implement, then run independent verifiers        → working code
/forge fix <change>     Correct course mid-stream, keep the chain aligned → aligned artifacts + code

Dispatch

Read the first argument as the phase verb. Read the matching reference file fully before acting — it is the step-by-step playbook for that phase.

If no verb is given, infer the phase from the request and confirm it. Never fail because a verb is missing or unknown. Common mappings:

specify takes a feature name. If absent, ask for one and derive a kebab-case slug.

Forge does not orchestrate phase transitions — you do. Start at any phase. A phase that finds no earlier artifacts gathers the minimum context it needs; each reference describes its own fallback.

Sizing

Every change is one of three sizes. The size controls how deep each phase goes and which phases are needed at all. See references/sizing.md for the full rubric.

The first phase to run picks the size and writes it to state.md. Size can only go up. Any later phase may promote it with a logged reason. A downgrade requires the user's confirmation — ratcheting prevents work from quietly skipping rigor a later phase already showed it needed. Each phase ends by listing which downstream phases the current size needs or lets you skip.

Artifacts and state

Artifact root (session CWD)

All ./.specs/* paths in this skill resolve against the session CWD — the directory the agent was invoked in — not the shell's current directory at the moment of the write. Subsequent cds do not move the artifact root.

At the start of every phase, resolve the artifact root once and reuse it. Capture the session CWD as an absolute path (pwd at the very first Bash call of the session, or the harness-provided starting directory) and set SPECS_ROOT="<abs>/.specs". Every read, write, mkdir, and ls inside this skill must go through $SPECS_ROOT/.... Never use a bare .specs/... after that resolution — a bare path would be interpreted against the current shell CWD and drift into a subfolder.

If the resolved root points inside another repo's .specs/ (e.g. the user invoked the skill from a nested package), stop and confirm with the user before writing.

All work for a change lives under ./.specs/<slug>/ (create it if missing):

./.specs/<slug>/spec.md       what & why (requirements, acceptance criteria, scope)
./.specs/<slug>/design.md     how (architecture, contracts, verification gates)
./.specs/<slug>/plan.md       tasks grouped into phases (parallel within a phase, AC-traced)
./.specs/<slug>/state.md      size, decisions log, task status, handoff — the source of truth
./.specs/<slug>/lessons.md    what went wrong here and the rule going forward

Templates for each are in templates/. state.md is the single source of truth. Re-read it at the start of every phase. Do not assume the runtime preserves its own internal state across phases — if it is not in state.md, it did not happen.

Acceptance criteria are written once, in spec.md, with stable IDs (PREFIX-NN). Design, plan, and execute reference those IDs; they never restate the criterion text.

Lessons

Each change keeps its own ./.specs/<slug>/lessons.md with ## Standing Rules (short imperatives, always loaded) and ## Log (tagged, append-only). Load it at the start of every phase. Append only when something non-obvious was learned: a hack, a gotcha, a corrected wrong assumption, a skipped gate. Routine success writes nothing. See references/lessons.md.

Orchestration (canonical — references should cite, not restate)

• Use subagents for parallel or heavy work. They run in Claude Code and OpenCode. They keep the main agent's context small and give independent perspectives (execute's verifiers depend on this).
• Workflow is an optional speed-up for dispatching many subagents at once, where the runtime supports it. Plain sequential subagent calls always work as a backup. Never require Workflow.
• Match model tier and reasoning effort to the task — don't pay frontier rates for mechanical work. See Model & effort selection below. This is the primary cost lever.
• One level of delegation. Subagents do not spawn subagents.
• Subagents are stateless. Put everything they need in the prompt (file paths, section refs, constraints). Outputs over ~100 lines go to a file; return the path, not the content.
• Prefer AskUserQuestion when available, with a recommended default per question. Fall back to a single plain-text question otherwise. Never bundle unrelated questions.

Model & effort selection (canonical — references cite, not restate)

Every subagent dispatch picks two dials. Set them explicitly per task; never let the whole fan-out default to the most expensive model. This is agent-agnostic — map the tiers to whatever your runtime exposes.

Tier — the model's capability class:

Pass the tier via the runtime's per-subagent model control (model on the Agent tool or Workflow agent(), model in a subagent definition's frontmatter, or the OpenCode agent's model field). If a runtime exposes no per-subagent model control, skip this dial and rely on effort alone — never block on it.

Effort — reasoning/thinking budget, where the runtime supports a reasoning-effort or thinking-budget setting: low for mechanical tasks, medium for ordinary work, high only for genuinely hard reasoning (adversarial refutation, ambiguous design). Where the runtime has no effort dial, fold the intent into tier choice.

Defaults by work type (start here, adjust for the specific task):

Size interacts with tier. A quick change should almost never dispatch a frontier subagent; a complex change earns frontier for its design and adversarial gates but still routes mechanical tasks to economy. When unsure between two tiers, pick the lower and let a failed gate promote it — the same ratchet as sizing.

Universal rules (apply to every phase)

State hygiene

1. Re-read state.md at the start of every phase. Write size, decisions, and status changes there as they happen, not at the end.

2. Write surgically. Edit only the target section — replace the content between its ## header and the next ## or end-of-file. Never regenerate the whole file or reorder sections; that silently clobbers append-only or update-in-place sections you did not mean to touch. Section write modes:

   Section	Write mode
   ## Decisions	append-only (never edit existing rows)
   ## Tasks	update-in-place (status, evidence)
   ## Validation delta	clear-on-resolve
   ## Verification evidence	append-on-PASS
   ## Handoff	overwrite

Honesty

3. Never claim a task or gate passed without running it. Done means you saw it pass, not that you believe it would.
4. Record honestly. Open questions, skipped gates, and assumptions stay visible. Never cover a gap with an invented answer.

Hand-off

5. Each phase finishes, reports, and recommends the next verb — it never runs the next phase. The one documented exception is fix: for a contained correction it re-aligns the artifacts and runs the code delta end-to-end in the same invocation (see references/fix.md); a larger correction still only recommends the phase chain.
6. /create-rfc and /create-adr are separate skills. Use /create-rfc when a significant decision needs stakeholder alignment; use /create-adr when an architectural choice deserves a standalone record. Reach for either at any point in the flow.