> Adapted from PRPs-agentic-eng by Wirasm. Part of the PRP workflow series.

# PRP Implement

Execute a plan file step-by-step with continuous validation. Every change is verified immediately — never accumulate broken state.

**Core Philosophy**: Validation loops catch mistakes early. Run checks after every change. Fix issues immediately.

**Golden Rule**: If a validation fails, fix it before moving on. Never accumulate broken state.

---

## Phase 0 — DETECT

### Package Manager Detection

| File Exists | Package Manager | Runner |
|---|---|---|
| `bun.lockb` | bun | `bun run` |
| `pnpm-lock.yaml` | pnpm | `pnpm run` |
| `yarn.lock` | yarn | `yarn` |
| `package-lock.json` | npm | `npm run` |
| `pyproject.toml` or `requirements.txt` | uv / pip | `uv run` or `python -m` |
| `Cargo.toml` | cargo | `cargo` |
| `go.mod` | go | `go` |

### Validation Scripts

Check `package.json` (or equivalent) for available scripts:

```bash
# For Node.js projects
cat package.json | grep -A 20 '"scripts"'
```

Note available commands for: type-check, lint, test, build.

---

## Phase 1 — LOAD

Read the plan file:

```bash
cat "$ARGUMENTS"
```

Extract these sections from the plan:
- **Summary** — What is being built
- **Patterns to Mirror** — Code conventions to follow
- **Files to Change** — What to create or modify
- **Step-by-Step Tasks** — Implementation sequence
- **Validation Commands** — How to verify correctness
- **Acceptance Criteria** — Definition of done

If the file doesn't exist or isn't a valid plan:
```
Error: Plan file not found or invalid.
Run /prp-plan <feature-description> to create a plan first.
```

**CHECKPOINT**: Plan loaded. All sections identified. Tasks extracted.

---

## Phase 2 — PREPARE

### Git State

```bash
git branch --show-current
git status --porcelain
```

### Branch Decision

| Current State | Action |
|---|---|
| On feature branch | Use current branch |
| On main, clean working tree | Create feature branch: `git checkout -b feat/{plan-name}` |
| On main, dirty working tree | **STOP** — Ask user to stash or commit first |
| In a git worktree for this feature | Use the worktree |

### Sync Remote

```bash
git pull --rebase origin $(git branch --show-current) 2>/dev/null || true
```

**CHECKPOINT**: On correct branch. Working tree ready. Remote synced.

---

## Phase 3 — EXECUTE

Process each task from the plan sequentially.

### Per-Task Loop

For each task in **Step-by-Step Tasks**:

1. **Read MIRROR reference** — Open the pattern file referenced in the task's MIRROR field. Understand the convention before writing code.

2. **Implement** — Write the code following the pattern exactly. Apply GOTCHA warnings. Use specified IMPORTS.

3. **Validate immediately** — After EVERY file change:
   ```bash
   # Run type-check (adjust command per project)
   [type-check command from Phase 0]
   ```
   If type-check fails → fix the error before moving to the next file.

4. **Track progress** — Log: `[done] Task N: [task name] — complete`

### Handling Deviations

If implementation must deviate from the plan:
- Note **WHAT** changed
- Note **WHY** it changed
- Continue with the corrected approach
- These deviations will be captured in the report

**CHECKPOINT**: All tasks executed. Deviations logged.

---

## Phase 4 — VALIDATE

Run all validation levels from the plan. Fix issues at each level before proceeding.

### Level 1: Static Analysis

```bash
# Type checking — zero errors required
[project type-check command]

# Linting — fix automatically where possible
[project lint command]
[project lint-fix command]
```

If lint errors remain after auto-fix, fix manually.

### Level 2: Unit Tests

Write tests for every new function (as specified in the plan's Testing Strategy).

```bash
[project test command for affected area]
```

- Every function needs at least one test
- Cover edge cases listed in the plan
- If a test fails → fix the implementation (not the test, unless the test is wrong)

### Level 3: Build Check

```bash
[project build command]
```

Build must succeed with zero errors.

### Level 4: Integration Testing (if applicable)

```bash
# Start server, run tests, stop server
[project dev server command] &
SERVER_PID=$!

# Wait for server to be ready (adjust port as needed)
SERVER_READY=0
for i in $(seq 1 30); do
  if curl -sf http://localhost:PORT/health >/dev/null 2>&1; then
    SERVER_READY=1
    break
  fi
  sleep 1
done

if [ "$SERVER_READY" -ne 1 ]; then
  kill "$SERVER_PID" 2>/dev/null || true
  echo "ERROR: Server failed to start within 30s" >&2
  exit 1
fi

[integration test command]
TEST_EXIT=$?

kill "$SERVER_PID" 2>/dev/null || true
wait "$SERVER_PID" 2>/dev/null || true

exit "$TEST_EXIT"
```

### Level 5: Edge Case Testing

Run through edge cases from the plan's Testing Strategy checklist.

**CHECKPOINT**: All 5 validation levels pass. Zero errors.

---

## Phase 5 — REPORT

### Create Implementation Report

```bash
mkdir -p .claude/PRPs/reports
```

Write report to `.claude/PRPs/reports/{plan-name}-report.md`:

```markdown
# Implementation Report: [Feature Name]

## Summary
[What was implemented]

## Assessment vs Reality

| Metric | Predicted (Plan) | Actual |
|---|---|---|
| Complexity | [from plan] | [actual] |
| Confidence | [from plan] | [actual] |
| Files Changed | [from plan] | [actual count] |

## Tasks Completed

| # | Task | Status | Notes |
|---|---|---|---|
| 1 | [task name] | [done] Complete | |
| 2 | [task name] | [done] Complete | Deviated — [reason] |

## Validation Results

| Level | Status | Notes |
|---|---|---|
| Static Analysis | [done] Pass | |
| Unit Tests | [done] Pass | N tests written |
| Build | [done] Pass | |
| Integration | [done] Pass | or N/A |
| Edge Cases | [done] Pass | |

## Files Changed

| File | Action | Lines |
|---|---|---|
| `path/to/file` | CREATED | +N |
| `path/to/file` | UPDATED | +N / -M |

## Deviations from Plan
[List any deviations with WHAT and WHY, or "None"]

## Issues Encountered
[List any problems and how they were resolved, or "None"]

## Tests Written

| Test File | Tests | Coverage |
|---|---|---|
| `path/to/test` | N tests | [area covered] |

## Next Steps
- [ ] Code review via `/code-review`
- [ ] Create PR via `/prp-pr`
```

### Update PRD (if applicable)

If this implementation was for a PRD phase:
1. Update the phase status from `in-progress` to `complete`
2. Add report path as reference

### Archive Plan

```bash
mkdir -p .claude/PRPs/plans/completed
mv "$ARGUMENTS" .claude/PRPs/plans/completed/
```

**CHECKPOINT**: Report created. PRD updated. Plan archived.

---

## Phase 6 — OUTPUT

Report to user:

```
## Implementation Complete

- **Plan**: [plan file path] → archived to completed/
- **Branch**: [current branch name]
- **Status**: [done] All tasks complete

### Validation Summary

| Check | Status |
|---|---|
| Type Check | [done] |
| Lint | [done] |
| Tests | [done] (N written) |
| Build | [done] |
| Integration | [done] or N/A |

### Files Changed
- [N] files created, [M] files updated

### Deviations
[Summary or "None — implemented exactly as planned"]

### Artifacts
- Report: `.claude/PRPs/reports/{name}-report.md`
- Archived Plan: `.claude/PRPs/plans/completed/{name}.plan.md`

### PRD Progress (if applicable)
| Phase | Status |
|---|---|
| Phase 1 | [done] Complete |
| Phase 2 | [next] |
| ... | ... |

> Next step: Run `/prp-pr` to create a pull request, or `/code-review` to review changes first.
```

---

## Handling Failures

### Type Check Fails
1. Read the error message carefully
2. Fix the type error in the source file
3. Re-run type-check
4. Continue only when clean

### Tests Fail
1. Identify whether the bug is in the implementation or the test
2. Fix the root cause (usually the implementation)
3. Re-run tests
4. Continue only when green

### Lint Fails
1. Run auto-fix first
2. If errors remain, fix manually
3. Re-run lint
4. Continue only when clean

### Build Fails
1. Usually a type or import issue — check error message
2. Fix the offending file
3. Re-run build
4. Continue only when successful

### Integration Test Fails
1. Check server started correctly
2. Verify endpoint/route exists
3. Check request format matches expected
4. Fix and re-run

---

## Success Criteria

- **TASKS_COMPLETE**: All tasks from the plan executed
- **TYPES_PASS**: Zero type errors
- **LINT_PASS**: Zero lint errors
- **TESTS_PASS**: All tests green, new tests written
- **BUILD_PASS**: Build succeeds
- **REPORT_CREATED**: Implementation report saved
- **PLAN_ARCHIVED**: Plan moved to `completed/`

---

## Next Steps

- Run `/code-review` to review changes before committing
- Run `/prp-commit` to commit with a descriptive message
- Run `/prp-pr` to create a pull request
- Run `/prp-plan <next-phase>` if the PRD has more phases