A tone of voice section in a brand book used to be short. Three adjectives. A line or two of clarification. Maybe a sentence-level example. Friendly but professional. Confident but not arrogant. The kind of guidance that worked because the people writing for the brand were trained writers who'd already absorbed the brand by osmosis.

It's getting longer. Sometimes a lot longer. Newer tone of voice documents being put together for smaller businesses are running to ten or fifteen pages, occasionally more. Specific vocabulary. Words to use, words to avoid. Sentence-length preferences. Punctuation conventions. Examples laid out as direct comparisons, on-brand next to off-brand, sometimes with annotations explaining what's different.

The reason is straightforward. The number of people producing copy for a small brand has gone up, and most of them aren't trained writers. The intern handling the LinkedIn account. The founder drafting a newsletter at midnight. The freelancer writing product copy. And now Claude or ChatGPT, asked to write a launch email in the brand's voice, fed whatever the person remembered to paste in at the top.

For that audience to produce consistent output, "warm but witty" isn't a useful instruction. It doesn't really mean anything. What you need is what warm but witty looks like on the page. Which words you'd use. Which you wouldn't. How long sentences tend to run. Whether you use semicolons. Whether you start sentences with And.

In practice the specificity ends up looking like a list of decisions. Sentence length tends to run between eight and eighteen words. Contractions are used. Oxford commas aren't. The brand says "we" more often than "I". It doesn't use exclamation marks except in direct speech. It avoids the word "just" as a hedge. None of these are surprising on their own. Read together, they describe a voice in a way three adjectives never could.

The same document also works as a system prompt. Pasted into the top of a conversation with Claude or ChatGPT, it gets you closer to on-brand output than any amount of asking nicely. A few of the better tone documents being written now are explicitly structured for that. The first few pages are written for humans, the next few are written in a format that reads cleanly when pasted into a tool. Not a separate document, just two passes through the same material.

That level of specificity used to feel pedantic. It now feels practical. The documents that are doing this well read more like style guides for a magazine than tone of voice paragraphs in a PDF. The reference point worth looking at is probably the Economist Style Guide or the New Yorker's internal style notes. Both lean heavily on the assumption that a voice is a set of accumulated small decisions, not a vibe.

There's a small risk in this that nobody talks about much. Writing the rules down makes them harder to break later. A tone of voice that was always slightly playful in a way the writers understood becomes a tone of voice that uses these eleven techniques to be playful. Once the techniques are listed, the brand starts to apply them like a checklist. Some of the warmth gets lost in the process of pinning it down. There isn't really a way around this, but it's worth being aware of when drafting.

There's an unexpected upside too. The level of specificity surfaces things about the brand that were never explicitly decided. Which words it would use. Which it wouldn't. It often takes writing those down to realise the brand had a stronger opinion than anyone had named.