Code Tour

---
name: code-tour
description: Create CodeTour `.tour` files — persona-targeted, step-by-step walkthroughs with real file and line anchors. Use for onboarding tours, architecture walkthroughs, PR tours, RCA tours, and structured "explain how this works" requests.
metadata:
  origin: ECC
---

# Code Tour

Create **CodeTour** `.tour` files for codebase walkthroughs that open directly to real files and line ranges. Tours live in `.tours/` and are meant for the CodeTour format, not ad hoc Markdown notes.

A good tour is a narrative for a specific reader:
- what they are looking at
- why it matters
- what path they should follow next

Only create `.tour` JSON files. Do not modify source code as part of this skill.

## When to Use

Use this skill when:
- the user asks for a code tour, onboarding tour, architecture walkthrough, or PR tour
- the user says "explain how X works" and wants a reusable guided artifact
- the user wants a ramp-up path for a new engineer or reviewer
- the task is better served by a guided sequence than a flat summary

Examples:
- onboarding a new maintainer
- architecture tour for one service or package
- PR-review walk-through anchored to changed files
- RCA tour showing the failure path
- security review tour of trust boundaries and key checks

## When NOT to Use

| Instead of code-tour | Use |
| --- | --- |
| A one-off explanation in chat is enough | answer directly |
| The user wants prose docs, not a `.tour` artifact | `documentation-lookup` or repo docs editing |
| The task is implementation or refactoring | do the implementation work |
| The task is broad codebase onboarding without a tour artifact | `codebase-onboarding` |

## Workflow

### 1. Discover

Explore the repo before writing anything:
- README and package/app entry points
- folder structure
- relevant config files
- the changed files if the tour is PR-focused

Do not start writing steps before you understand the shape of the code.

### 2. Infer the reader

Decide the persona and depth from the request.

| Request shape | Persona | Suggested depth |
| --- | --- | --- |
| "onboarding", "new joiner" | `new-joiner` | 9-13 steps |
| "quick tour", "vibe check" | `vibecoder` | 5-8 steps |
| "architecture" | `architect` | 14-18 steps |
| "tour this PR" | `pr-reviewer` | 7-11 steps |
| "why did this break" | `rca-investigator` | 7-11 steps |
| "security review" | `security-reviewer` | 7-11 steps |
| "explain how this feature works" | `feature-explainer` | 7-11 steps |
| "debug this path" | `bug-fixer` | 7-11 steps |

### 3. Read and verify anchors

Every file path and line anchor must be real:
- confirm the file exists
- confirm the line numbers are in range
- if using a selection, verify the exact block
- if the file is volatile, prefer a pattern-based anchor

Never guess line numbers.

### 4. Write the `.tour`

Write to:

```text
.tours/<persona>-<focus>.tour
```

Keep the path deterministic and readable.

### 5. Validate

Before finishing:
- every referenced path exists
- every line or selection is valid
- the first step is anchored to a real file or directory
- the `ref` points at a branch or commit that actually has every file the tour references (see below)
- the tour tells a coherent story rather than listing files

## The `ref` Field

`ref` ties the tour to a git branch or commit. It matters more than it looks: when `ref` is not the branch the reader has checked out, CodeTour opens each step's file from that revision in git, not from the files on disk. If a file is not in that revision, the step will not open — the reader sees *"The editor could not be opened because the file was not found"* even though the file is sitting right there. The tour and its comments still show, so the real cause is easy to miss.

Pick `ref` by tour type:

| Tour type | Set `ref` to |
| --- | --- |
| PR tour | the PR branch — never the base branch |
| Onboarding / architecture | the branch the reader will be on (often `main`), or leave it out |
| Not sure | leave `ref` out, so CodeTour reads files straight from disk |

The PR case is the common trap: a PR usually adds new files, and new files do not exist on the base branch yet. Point `ref` at the base (e.g. `develop`) and every step on a new file fails to open.

Before finishing, confirm each step's file actually exists at the `ref` you chose.

## Step Types

### Content

Use sparingly, usually only for a closing step:

```json
{ "title": "Next Steps", "description": "You can now trace the request path end to end." }
```

Do not make the first step content-only.

### Directory

Use to orient the reader to a module:

```json
{ "directory": "src/services", "title": "Service Layer", "description": "The core orchestration logic lives here." }
```

### File + line

This is the default step type:

```json
{ "file": "src/auth/middleware.ts", "line": 42, "title": "Auth Gate", "description": "Every protected request passes here first." }
```

### Selection

Use when one code block matters more than the whole file:

```json
{
  "file": "src/core/pipeline.ts",
  "selection": {
    "start": { "line": 15, "character": 0 },
    "end": { "line": 34, "character": 0 }
  },
  "title": "Request Pipeline",
  "description": "This block wires validation, auth, and downstream execution."
}
```

### Pattern

Use when exact lines may drift:

```json
{ "file": "src/app.ts", "pattern": "export default class App", "title": "Application Entry" }
```

### URI

Use for PRs, issues, or docs when helpful:

```json
{ "uri": "https://github.com/org/repo/pull/456", "title": "The PR" }
```

## Writing Rule: SMIG

Each description should answer:
- **Situation**: what the reader is looking at
- **Mechanism**: how it works
- **Implication**: why it matters for this persona
- **Gotcha**: what a smart reader might miss

Keep descriptions compact, specific, and grounded in the actual code.

## Narrative Shape

Use this arc unless the task clearly needs something different:
1. orientation
2. module map
3. core execution path
4. edge case or gotcha
5. closing / next move

The tour should feel like a path, not an inventory.

## Example

```json
{
  "$schema": "https://aka.ms/codetour-schema",
  "title": "API Service Tour",
  "description": "Walkthrough of the request path for the payments service.",
  "ref": "main",
  "steps": [
    {
      "directory": "src",
      "title": "Source Root",
      "description": "All runtime code for the service starts here."
    },
    {
      "file": "src/server.ts",
      "line": 12,
      "title": "Entry Point",
      "description": "The server boots here and wires middleware before any route is reached."
    },
    {
      "file": "src/routes/payments.ts",
      "line": 8,
      "title": "Payment Routes",
      "description": "Every payments request enters through this router before hitting service logic."
    },
    {
      "title": "Next Steps",
      "description": "You can now follow any payment request end to end with the main anchors in place."
    }
  ]
}
```

## Anti-Patterns

| Anti-pattern | Fix |
| --- | --- |
| Flat file listing | Tell a story with dependency between steps |
| Generic descriptions | Name the concrete code path or pattern |
| Guessed anchors | Verify every file and line first |
| Too many steps for a quick tour | Cut aggressively |
| First step is content-only | Anchor the first step to a real file or directory |
| Persona mismatch | Write for the actual reader, not a generic engineer |

## Best Practices

- keep step count proportional to repo size and persona depth
- use directory steps for orientation, file steps for substance
- for PR tours, cover changed files first
- for monorepos, scope to the relevant packages instead of touring everything
- close with what the reader can now do, not a recap

## Related Skills

- `codebase-onboarding`
- `coding-standards`
- `council`
- official upstream format: `microsoft/codetour`