explain-flow

name	explain-flow
description	Explain how code flows with concrete input/output examples, ASCII diagrams, and before/after tables. Works on PRs, functions, modules, or any code path. Triggers: /explain-flow, "explain this PR", "explain this function", "explain this module", "how does this flow", "walk me through", "explain the change in"

/explain-flow — Explain Code with Concrete Examples

Produce a clear explanation of how data flows through a PR, function, or module. The goal is to build the reader's mental model first, then confirm it with code — not to narrate the diff line by line.

Step 1 — Gather the source material

• PR: gh pr view and gh pr diff. Read all changed files.
• Function: Read the function and its callers/callees one level in each direction.
• Module/package: Read the public API surface and key internal wiring.

For PRs and refactors, understand what the code did before the change and what it does after before writing anything.

Step 2 — Write the explanation

Work through these sections in order. Each one builds on the last.

Background

Orient the reader before touching the code. Assume no prior knowledge of the surrounding system. Cover:

• What the surrounding system does (one short paragraph)
• What was missing, broken, or constrained that prompted this change
• Any architectural rules or design decisions that shaped the approach

Intuition

Explain the 2–4 core ideas in the change before showing any real code. Use toy examples and analogies. For each concept:

• Name it
• Make it concrete with a minimal before/after or a simple example
• State why it matters

This section should make the Code section feel like confirmation rather than discovery. Don't front-load implementation detail here — that belongs in the next section.

Code walkthrough

One-paragraph summary of what the change does and why, then a step-by-step trace through the key code path using realistic example data. Show actual values at each step:

Input: GET /api/items?filter=active
  1. Parse filters      → { status: "active" }
  2. Check permissions  → { orgIDs: ["org-1"], tenantIDs: ["t-1"] }
  3. Query DB           → SELECT ... WHERE status='active' AND org_id IN ('org-1')
  4. Return             → [{ id: "item-1", status: "active" }]

When a transformation spans multiple steps, show the data in both old and new form at each step — not just the endpoints. The reader should see the value mutating stage by stage.

When there are meaningful branches, add a decision matrix:

| Input condition       | Path taken     | Result          |
|----------------------|----------------|-----------------|
| flag ON + authorized | new + old path | union of both   |
| flag OFF             | old path only  | legacy behavior |
| neither authorized   | early return   | empty response  |

Other changes (PRs only)

Briefly list mechanical or supporting changes — test updates, config, helpers — that don't affect the core flow.

Guidelines

• Use realistic field names and values from the actual code, not generic placeholders.
• Keep examples short but complete: enough to see the transformation, not every field.
• Prefer ASCII flow notation over prose for multi-step pipelines.
• Pick the 2-3 most important code paths; don't trace every branch.
• For modules, lead with the happy path, then note error/edge cases.