Plain language

Plain language is writing the audience can understand the first time they read it. The framework here comes from digital.gov's Plain Language Guide series, which carries forward the federal guidelines behind the Plain Writing Act of 2010. The Act defines plain writing as "clear, concise, well-organized, and follows other best practices appropriate to the subject or field and intended audience."

The point is not to dumb things down. It is to spend the reader's attention on the message instead of on decoding the sentence.

Two modes

Document mode. You are producing text that will live somewhere: a report, proposal, README, email, memo, web page, release note, policy. Apply everything below, and read the relevant reference file when the piece is long or the stakes are high.

Conversation mode. You are replying to the user in session. The same rules apply, scaled to the size of a reply. See "Replying in chat" near the end.