Period drama is having a moment: Wikipedia's article on this year's film adaptation of an 1811 novel went from about 5,800 to about 28,700 daily views between September 20 and October 18, 2026 (Wikimedia pageviews).
Say it the way they wrote in 1811.
Paste a text, a quick email or a thank-you. Get it back as a letter with Regency manners - a salutation, courtesies, a closing fit for whoever it is for - built only from what you wrote. Before anyone reads it, the message gets a verdict: most proper, a trifle forward, scandalous, or wants more.
I The message
The sweep
Word for word (the page's own swaps - not the letter)
II The sheet
III Write the letter
The model writes only from your message - no people, places, dates, gifts or plans you did not mention, and no carriages or candles of its own. A modern thing you named gets a period stand-in, and every swap is listed. A line that mocks or gossips about someone is struck out, not softened; a message that says nothing yet gets questions back instead of a letter.
IV Kept letters
About the post, then
A Regency letter was usually a single sheet folded into its own packet - there were no envelopes in ordinary use - and closed with a wax seal or a wafer. In Britain before the penny post of 1840 the recipient usually paid, by distance and by the number of sheets, so writers sometimes turned the page sideways and wrote across their own lines: a crossed letter. The closings here (affectionate for friends and family, devoted for a sweetheart, sincere for an acquaintance, "your most obedient servant" for business) follow the period's habits; the words in between are your own.