There is no download

For months a small app has been running at the edge of my screen. It's called peek — a native macOS markdown viewer. You run peek notes.md, a window opens, and the document renders with warm, book-like typography. Save the file and the window updates in place: same pixel of scroll, no flash, and — this is the part I care about — no stolen focus.

The way I actually use it is as a hook in Claude Code. Every markdown document the agent writes gets handed to peek, so rendered documents accumulate quietly beside my terminal in case I want to read them. That workflow shaped the design more than anything else. Passivity is a hard requirement — a window opened by a hook must never interrupt the session — and every invocation is its own process with its own window, so the documents pile up instead of replacing each other.

The release

Today I'm releasing peek. There is no download. There is no source code either, and there never will be. The release is peek-commons — a Commons Format module: a prose specification of intent, seventeen named constraints, an interface contract, a threat model where the adversary is the document rather than the network, and a suite of twenty-eight conformance evals. If you want peek, you generate your own.

If that sounds backwards, the argument is in two earlier essays. In OSS has moved to a Dark Forest I argued that shared code has become a shared attack surface — one model-discovered exploit amortizes across every machine running the same bytes. In Save the OSS Commons with a Format I proposed the move: don't share code, share specs and evals, and generate everything. peek-commons is me taking my own advice. It is the first real module I've published that isn't the format's own tooling, and the code I run stays on my machine.

Generate your own

The mechanics are short. Hand commonsformat.md to a capable model, along with the visual spec it references. Generate in whatever language you like — the module pins macOS and WebKit, deliberately, but says nothing about what the code looks like. Then run the implementation against evals.toml. Functional cases passing is tier D0. Adversarial cases passing, with every constraint covered, is D1 — the tier the module targets. The adversarial cases are where the contract lives: script injection that must not execute, a document full of remote references that must produce zero network requests, a burst of fifty saves that must converge without stealing focus.

Your peek will not be byte-identical to mine. That's the point. Divergent implementations of the same contract are what breaks the economics of the dark forest. Where it matters — and the evals define exactly where it matters — your peek and mine agree.

What the spec taught me

Writing the module forced decisions the code had never made me state. The binary quietly opened a new window per invocation; nothing anywhere said it must, until the hook workflow made me realize a generated single-window peek would be broken in a way no functional test would catch. That's now a constraint with an eval. The threat model was the same: I knew the document was untrusted, but I had never written down what that meant until the spec demanded it.

Next month I need peek on a work machine. I won't copy the binary. I'll point a model at the module, generate a fresh implementation, and run the evals. The window opens. The code stays home.