In short
Text with no hidden formatting. What you see is all there is. The most durable format there is.
Plain text is characters and nothing else. No fonts, no invisible styles, no proprietary wrapper. A .txt file from 1985 opens today and will open in 2050.
We write instructions for agents in plain text and Markdown because both are readable by any person and any program, they diff cleanly when they change, and they cannot hide anything. If an instruction is in the file, you can see it. If it is not, the agent does not have it.
The opposite is a document that looks simple and carries a hundred formatting decisions underneath. Agents are worse at those, and so are the people who inherit them.
Example
What it looks like.
plain-text.mdplain text
A trust-boundaries file, in full:May read: the shared drive, the CRM, the calendar.May write: drafts, the CRM, the blog.Never: send an email, move money, touch credentials.
Related
Read next.
- MarkdownPlain text with a few marks for structure. Humans read it, machines parse it. It is the language we write instructions in.Read the definition
- instruction fileThe Markdown file that tells an agent who it is, what it owns, and what it may never do. The agent's job description, readable by the agent.Read the definition
- program in txt and mdThe instructions are the code. Write what you want in plain language, keep it in a file, update the file forever. No Python, no Bash.Read the definition