When to use it
Use it when an email has a lot of detail but one clear ask. Start with a one-line summary of what you need and by when. Busy readers can act right away, and anyone who wants the details can keep reading.
Example
You: “TL;DR: I need your approval by Friday. Details below.”
Director: “Approved. Read the summary, looks good.”
In an email or Slack message
In Slack, put the ask in the first line and the details in a thread reply. If your audience doesn't use “TL;DR”, “Summary:” or “Short version:” works just as well.