A README is the front-door note of a repository: the first file to read when you open a repo and feel lost. It’s an orientation more than a technical spec, answering who this is for, what’s in here, how to run it, and how to change it safely. Most are written in markdown, plain structured text with headings and lists, which makes them easy to read on GitHub and easy for agents to parse.
An office building lobby makes this concrete. A good lobby has a directory, a reception desk, and a sign for which floor each company is on. Without it, you’re wandering hallways and guessing.
Why you care
For agent work, a README acts like lightweight project instructions for humans and AI: it tells a new person or a fresh session how to start without asking ten setup questions. A good one stays a doorway, answering a serious reader’s first questions and pointing to the deeper docs rather than carrying every detail. A repo without a useful README wastes attention, because every new person and every new AI session has to rediscover the same basics.