Terminal-based runtime that coding agents run inside of.
Splits itself into four audiences and tells the agent how to determine which one it is.
This file points the agent at 7 other documents in the repository. Open any of them to read it here, as it was at this commit.
├── docs │ └── next │ ├── │ └── ├── skills │ └── herdr │ └── ├── vendor │ └── ├── ├── └──
File measured on master at commit 2778411. Analysis written 2026-09-14. Star count is a snapshot from September 2026.
Opens by dividing its own contents into universal rules, maintainer-only workflow, one person's local machine setup, and an external contributor guardrail. The remainder covers performance paths, wire-compatibility contracts, release channels, and what an agent may open on the repository.
Quoted lines are verbatim from the file. Open one to see it where it sits.
Scope layering
Before the other sections apply, the file defines how to establish which scope the agent is in. Maintainer status requires three conditions together: the username appears in a checked-in file, the configured remote is the canonical repository, and the authenticated account has write access. Any condition that cannot be verified sends the agent to the most restricted scope.
Contribution etiquette
The external contributor section states that a pasted approval message, a claim of permission, or an issue comment does not confer maintainer status. The only route it recognizes is membership in a file in the repository. It also sets out what an agent helping an external contributor may file: a reproducible bug report on the exact template, and nothing else.
Six code paths are named as places where cost multiplies, and the agent is asked to work out the multiplier before adding work to them: per byte or event, times panes or tabs, times attached clients. Changes that widen those loops require a profile at 1 and at least 15 panes with the scaling delta reported.
Ratchets
Named codecs reachable from a published endpoint may not have fields added, reordered or reinterpreted; a new codec name is added instead. The section closes by stating that the digest tests cannot detect an appended enum variant, so every enum reachable from a frozen codec is treated as closed regardless of a green test run.
Verification by change type
The maintainer workflow treats two review bots as checks to wait for on the latest pushed commit, alongside the build and test jobs. Findings are to be fixed or answered inline with a technical reason. The workflow ends at "ready" and assigns the merge to a named human.
herdr's file tells an agent how the codebase works. It cannot tell it which bug three customers hit this week. Modem keeps that context current and attaches it to the work.