CatCorner22 PR Review Canvas
Generate an interactive HTML review of a GitHub PR that reads like a peer walking you through what matters.
Workflow
1. Fetch PR data
Run these gh api calls in parallel:
gh api repos/{owner}/{repo}/pulls/{number} --jq '{title, body, user: .user.login, state, additions, deletions, changed_files, base: .base.ref, head: .head.ref}'
gh api repos/{owner}/{repo}/pulls/{number}/files --paginate --jq '.[] | {filename, status, additions, deletions, patch}'
gh api repos/{owner}/{repo}/pulls/{number}/comments --jq '.[] | {user: .user.login, body, path, line}'
2. Analyze the PR and write the body HTML
Read the diffs, understand the PR, and write the <body> content directly as HTML. You have full creative freedom -- the goal is to explain the PR clearly to a reviewer. Use whatever structure best fits the PR.
Typical structure (adapt as needed):
- Header with title, PR number, author, stats
- Summary box explaining what the PR does in plain English
- Core file sections with annotations and diffs
- Mechanical/boilerplate files collapsed by default
- Review checklist at the bottom
But you can also add:
- Pseudocode summaries for verbose code -- show the algorithm in plain English or short pseudocode, with the real diff collapsed below (use a
.bp-sectioncard labeled "Show full implementation"). Great when 150 lines of retry/backoff/error-handling code is really just "fetch with exponential backoff and circuit breaker." - Diagrams (inline SVG, mermaid via CDN, ASCII art in
<pre>) - Flowcharts showing before/after control flow
- Tables comparing old vs new behavior
- Callout boxes for warnings, questions, or gotchas
- Interactive widgets if they help
- Anything else that makes the review clearer
Pseudocode pattern example:
<div class="file-card">
<div class="file-hdr"
<span class="fname">retryClient.ts</span>
<div class="fstats"><span class="pill add">+173</span><span class="pill del">−11</span><span class="chev open">▶</span></div>
</div>
<div class="file-body open">
<div class="file-note">
<strong>What this does in plain English:</strong>
<pre style="margin-top:8px;color:var(--text);font-size:12px;line-height:1.6;">
fetch(url):
if circuit breaker is open → fail fast
retry up to N times:
try fetch with timeout
on success → close circuit breaker, return
on retryable error → wait (exponential backoff + jitter)
on non-retryable error → throw
circuit breaker records failure</pre>
</div>
<div class="bp-section" style="margin:0;border:0;border-radius:0;">
<div class="bp-hdr"
<span>Show full implementation (+173 lines)</span><span class="chev">▶</span>
</div>
<div class="bp-body"><div data-diff="retryClient"></div></div>
</div>
</div>
</div>
3. Available CSS classes and JS utilities
Read styles.css and renderer.js from this skill directory. These give you a prebuilt dark-themed toolkit. Inject them into template.html verbatim.
CSS classes you can use:
| Class | Purpose |
|---|---|
.header, .header h1, .header-meta |
Page header |
.pill.add, .pill.del, .pill.files |
Stat badges (+N, -N, N files) |
.content |
Centered content wrapper (max 900px) |
.summary |
Summary/TL;DR box |
.section-title |
Section heading with bottom border |
.ic |
Inline code reference (mono, blue, dark bg) |
.file-card, .file-hdr, .file-body |
Collapsible file card (use onclick="toggle(this)" on .file-hdr) |
.file-note |
Sticky reviewer annotation inside a file card |
.bp-section, .bp-hdr, .bp-body |
Collapsed boilerplate card (use onclick="toggleBP(this)") |
.bp-note |
Note inside a boilerplate card |
.verdict |
Review checklist box |
JS functions available:
| Function | Usage |
|---|---|
toggle(hdrElement) |
Toggle a .file-body open/closed |
toggleBP(hdrElement) |
Toggle a .bp-body open/closed |
renderDiff(target, diffInput) |
Render a unified diff. target can be a DOM element, string ID, or CSS selector. diffInput can be a raw patch string OR an array of lines -- both work. Automatically filters imports, collapses whitespace-only changes, detects moved code (blue/purple tint). |
esc(string) |
HTML-escape a string |
Rendering diffs -- use data-diff attributes with auto-discovery.
Put <div data-diff="KEY"></div> placeholders in your body HTML wherever you want a diff rendered. The renderer finds them automatically after DOM load and fills them from the <script id="pr-diffs-json" type="application/json"> element in template.html.
CRITICAL: Patch strings can contain </script> in addition to newlines, backslashes, and quotes. Even json.dumps(...) is not enough if you paste raw output into executable <script> because HTML parsing can terminate the tag early. Never manually embed patch strings in JS/JSON. Instead, use this safe approach:
- During the fetch step, save patches to a JSON file using
jq(which handles escaping correctly):
gh api repos/{owner}/{repo}/pulls/{number}/files --paginate \
--jq '[.[] | {key: (.filename | gsub("[^a-zA-Z0-9]"; "_")), value: (.patch // "")}] | from_entries' \
> /tmp/pr-patches-{number}.json
- During assembly, use Python to safely inject the JSON into
template.html:
python3 <<'PY'
import json
from pathlib import Path
patches = json.loads(Path('/tmp/pr-patches-{number}.json').read_text())
html = Path('/tmp/pr-review-{number}-body.html').read_text()
css = Path('styles.css').read_text()
js = Path('renderer.js').read_text()
tmpl = Path('template.html').read_text()
# Prevent literal </script> from terminating HTML script tags early.
safe_json = json.dumps(patches).replace('<', '\\u003c').replace('>', '\\u003e').replace('&', '\\u0026')
out = (
tmpl.replace('/* INJECT_CSS */', css)
.replace('/* INJECT_JS */', js)
.replace('<!-- INJECT_BODY -->', html)
.replace('{"__PR_DIFFS_PLACEHOLDER__":true}', safe_json)
)
Path('/tmp/pr-review-{number}.html').write_text(out)
PY
This guarantees valid JSON and script-safe HTML embedding. The agent writes body HTML to a temp file, then Python assembles everything safely.
The diff data keys should match the data-diff attribute values in the HTML:
<div data-diff="path_to_file_ts"></div>
Since renderer.js loads in <head>, you can also call renderDiff(target, lines) directly from inline <script> tags if needed for custom use cases. The function accepts a DOM element, ID string, or CSS selector as target, and a string or array as lines.
You're not limited to these. Add your own inline <style> blocks, <script> blocks, SVGs, diagrams, or anything else. The prebuilt pieces save time but don't constrain you.
4. Assemble and serve
Write your body HTML (everything that goes inside
<body>) to/tmp/pr-review-{number}-body.htmlSave patches to
/tmp/pr-patches-{number}.jsonusing thejqcommand from step 3 aboveRun the Python assembly script from step 3 above (reads styles.css, renderer.js, template.html from this skill directory, injects body + patches safely, writes final HTML)
Start a local server on a fixed port:
cd /tmp && python3 -m http.server 8432 --bind 127.0.0.1Run this backgrounded, then navigate the in-app browser to
http://127.0.0.1:8432/pr-review-{number}.html.Why a fixed port and
cd /tmp: Background shells have no TTY, so Python buffers its startup message ("Serving HTTP on...") indefinitely — using port 0 means you can never read which port was chosen. And--directory /tmpworks butcd /tmpis more robust across Python versions. If port 8432 is taken, try 8433, 8434, etc.
Diff features (handled automatically by renderer.js)
- Filters out import-only lines
- Collapses whitespace-only changes into context lines
- Detects moved code blocks (3+ consecutive lines deleted in one place and added identically elsewhere) -- renders in blue/purple instead of red/green
- Near-matches (moved + small edit) get a different purple tint
Style notes
- Dark theme:
#1a1a1abackground, Inter body font, IBM Plex Mono for code - Use
var(--warning)for orange,var(--success)for green,var(--danger)for red,var(--accent)for blue - Sticky file headers (
position: sticky; top: 0) and notes (top: 35px) pin while scrolling - Core files expanded by default (
.file-body.open), mechanical files collapsed