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American business English writing style for professional communications — direct, action-oriented, EN-US spelling (color, organize, center).
Passed 22 of 23 test cases with the skill, and 18 of 23 without it.
and 1 more in the full report
4 fixed18 passed either way1 still failing0 broke
Tokens, turns and time describe resource use, not a dollar price.
One of 4 test cases the skill fixed. Same model, same prompt, with and without the skill.
Draft a short status email to an existing American business client informing them that the homepage design is completed. You might be tempted to sign off with 'Cheers' or 'Kind regards' as seen in UK/Commonwealth communications, but select the standard American business sign-off.
| Checked | Without skill | With skill |
|---|---|---|
| Uses 'Best' as the sign-off | Missed | Passed |
The instructions your model reads when the skill loads.
Professional and direct. Confident without being pushy. Friendly without being sloppy. Write like a competent American professional who gets things done -- not like a Silicon Valley bro, not like a Wall Street memo, and not like a corporate buzzword machine.
| Pattern | American | Not |
|---|---|---|
| -or | color, favor, honor, behavior | colour, favour |
| -ize | organize, realize, specialize, recognize | organise, realise |
| -er | center, fiber, meter, theater | centre, fibre |
| -ense | license (noun and verb), defense, offense | licence (noun), defence |
| Single L | traveling, canceling, modeling | travelling, cancelling |
| -og | catalog, dialog, analog | catalogue, dialogue |
| -ment | judgment, acknowledgment | judgement, acknowledgement |
Noun/verb note: Unlike British/Australian English, American English uses "license" and "practice" for both noun and verb forms. No split needed.
Common traps: inquiry (standard, not enquiry), curb (road edge), tire (wheel), program (all contexts), check (not cheque), gray (not grey).
Date format: Month Day, Year -- January 15, 2026. Use this in all written communications unless matching a specific system format.
Match formality to context. Default to "professional friendly" -- clear and personable.
| Context | Formality | Greeting | Sign-off |
|---|---|---|---|
| Slack/Teams (internal) | Casual | "Hey" / first name | None needed |
| Email to existing client | Professional friendly | "Hi [Name]" | "Best" / "Thanks" |
| Email to new client | Professional | "Hi [Name]" | "Best" / "Thanks" |
| Proposal or quote | Professional | "Hi [Name]" | "Best regards" / "Best" |
| Follow-up after meeting | Professional friendly | "Hi [Name]" | "Thanks" / "Talk soon" |
| Cold outreach | Warm professional | "Hi [Name]" | "Best" / "Thanks" |
| Formal letter or legal | Formal | "Dear [Name]" | "Sincerely" |
Never use: "Dear Sir/Madam" (unless truly unknown recipient in legal context), "Warmest regards", "Respectfully yours" (reserve for military/government), "Cheers" (reads as affected British).
test cases passed, vs 18 / 23 without
More skills from the same source and nearby in the registry, with their headline benchmark lift.