Marginalia
Vol. I · No. 001

A careful reader for your codebase.

Marginalia reviews every pull request the way a senior engineer would — patiently, in the margins, with reasoning you can follow.

Read a sample review Install for GitHub →
Reads your codebase, not just the diff Annotates in plain English Never nitpicks what your formatter handles
PR #482 · checkout — fix rounding on split carts 3 notes
1export async function getCartTotal(userId) {
21 const cart = await db.carts.findOne({ userId });
3 let total = 0;
4 for (const item of cart.items) {
52 total += item.price * item.quantity;
6 }
73 return total;
8}
What it notices

The four things a good reviewer always reads for.

Marginalia is trained not to be exhaustive, but to be accurate about what actually matters in a review. Four axes; nothing more.

Every note carries its axis, its reasoning, and — where useful — a small suggestion. You can accept, thank, or dismiss it, and Marginalia learns.

  1. On correctness — i.

    Race conditions, null derefs, off-by-one arithmetic, requests that can silently drop. The kind of bug that's obvious in hindsight but takes a careful read to see.

  2. On clarity — ii.

    Misleading names, missing units, functions doing three things, tests that quietly test the wrong condition. The kind of thing that a linter cannot catch because it is not a rule.

  3. On kindness — iii.

    Small suggestions to the next reader — a clearer variable name, a comment that saves an hour of archaeology. Framed as offers, not requirements.

  4. On restraint — iv.

    What Marginalia will not do: nitpick style your formatter already owns, rewrite your architecture in a comment, or repeat itself across six threads. Silence is a review too.

The method, in three parts

How it reads.

A review is a sequence — first understand the whole, then attend to the change, then talk about it. Marginalia keeps that order.

Plate i.

Comprehension

Marginalia reads your codebase before the pull request. It learns your conventions, your names, your quiet norms — the sort of thing a new hire absorbs over months.

Plate ii.

Attention

When a pull request opens, Marginalia looks at the diff in the context of what it already knows. It attends to the change, not the file.

Plate iii.

Conversation

Notes arrive in the margin of the diff, with reasoning you can follow. You reply, disagree, or accept. Marginalia keeps its silence when there's nothing to say.

For a year we watched our best senior engineer's review comments get shorter, and our juniors' pull requests get better. Marginalia does the same shift in reading, at the pace of every commit.
Tomás Fernández — Head of Engineering, Foundry & Tap
Subscription

Two tiers. Cancel any month.

Marginalia is priced per developer, per month. Public repositories are always free — we started there ourselves.

Reader

Free  for public repositories & solo work
  • Unlimited reviews on public repositories
  • One private repository, personal account
  • Full margin-annotation UX
  • Community support
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Editor

$14  per developer, per month
  • Unlimited private repositories
  • Marginalia learns your team's conventions
  • SSO, audit log, IP allowlist
  • Review-quality analytics, without leaderboards
  • Priority support, weekday hours
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