Copy breaks two ways: it contradicts the product's own vocabulary, or it is assembled so it cannot be translated. Both are visible in the code before anyone reads the screen. copy-voice sets the voice; this node is how the strings are found, built and formatted.

Inventory before writing

Find where the copy lives first: the translation call (t(, i18n., <FormattedMessage, $t() and its catalogues (locales/**/*.json, messages/*.json, *.po, *.strings), or a CMS or API. List the noun used for each object and the verb for each action — "project" or "workspace", "Delete" or "Remove" — and the case used per element type. New copy uses those words. A synonym is a finding only where one thing is now named two ways: if it is "Archive" in the menu it is not "Move to storage" in the toast.

A multi-step flow uses one vocabulary end to end: "Get started" to enter, "Continue" or "Next" to advance, "Done" to finish.

Build strings whole

Never assemble a sentence around a variable — "You have " + n + " new messages" — because word order changes per language. Write one message with placeholders, and never n === 1 ? "" : "s": many languages have more than two plural forms.

inbox.count = {count, plural,
  =0 {No new messages}
  one {# new message}
  other {# new messages}
}

=0 matches zero exactly; one and other are categories, and a translator adds few or many where the language needs them. Without a library, new Intl.PluralRules(locale).select(count) picks the category.

Format through Intl, with the user's locale

Value	Call
Currency	`Intl.NumberFormat(locale, { style: "currency", currency })`
Unit	`Intl.NumberFormat(locale, { style: "unit", unit: "megabyte" })`
Date	`Intl.DateTimeFormat(locale, { dateStyle: "medium" })`
Relative time	`Intl.RelativeTimeFormat(locale, { numeric: "auto" })` → "yesterday"
List	`Intl.ListFormat(locale, { type: "conjunction" })` — never join with `", "` and `" and "`

toLocaleDateString() with no locale, or a date built from getMonth(), is the finding. Translated strings grow — a one-word button grows most — so the container rules are in growth-and-overflow.

Labels that do their job

Buttons start with a verb naming the action: "Send", "Save draft", "Delete project" — never "OK" or "Let's go!". An icon button's accessible name follows the same rule: "Delete project", never "Trash icon" (screen-reader-announcements).
Links name their destination out of context: "Read the billing docs", not "Click here". Two bare "Learn more" on one page each get a suffix: "Learn more about exports".
Toggles describe the ON state. "Send read receipts", never "Don't send read receipts", which makes the switch a double negative. Link straight to a referenced setting instead of narrating its path.
Address the reader as "you"; in errors, "we" reads as deflection. Possessives sparingly — "Favorites" beats "Your favorites" — and never "My account" beside "Your settings".
Match the device: "tap" on touch, "click" with a pointer, "select" when both.

Status copy stays parallel

State	Pattern
In progress	`-ing` verb + object: "Saving changes…"
Done	object + past tense, no "successfully": "Changes saved"
Failed	what did not happen, then the next step: "Changes not saved. Check your connection and try again."
Unavailable	why, beside the control: "Add a payment method to publish"
Partial	both counts: "9 of 12 files uploaded. Retry 3 failed files"

"Saving changes…" resolves to "Changes saved" — same object, same order. Cut "Please" from routine instructions.

Gotcha

A placeholder is an example in the accepted format — name@example.com, DD/MM/YYYY — never an instruction and never the label (forms-behavior). And a deliberate brand voice is not a defect: reword only where copy is inconsistent, ambiguous, untranslatable or wrong for the stakes.

Sources

Jakub Krehel, interfaces skills (MIT, github.com/jakubkrehel/skills, HEAD 592aedc, read 2026-10-25): skills/better-writing/SKILL.md (Inventory the existing strings first, Build strings whole, Verb-first buttons, Links describe their destination, Settings describe the ON state), patterns.md (status copy, plurals, locale formatting).
Unicode ICU MessageFormat; ECMA-402 Intl.
Related: copy-voice, copy-tells, destructive-actions, interfaces-reconciliation.