The shortlist
5 things that do it. Ours is in there, labelled, not on top.
Where one of our products fits, it sits in the list with an "ours" label, never forced to the top. Ours: made by the same studio that runs this site.
Standing instructions applied to all chats, plus optional Memory that can use past chats and saved memories.
- Free
- Custom instructions are on all plans (vendor help page); Memory is limited on Free per the pricing page.
- Paid
- price not checked
- Best at
- Setting a standing tone once and having it applied to every chat.
- The catch
- You describe your style yourself, within a limit: 1,500 characters on Free and Go, 5,000 on Plus, Pro, Business and Education. The help page does not say it measures your writing.
- web
- desktop
- ios
- android
Account-wide "Instructions for Claude", per-project instructions and skills that can "apply communication patterns based on your own writing or preferences".
- Free
- A free plan exists, with Pro at the price shown (Claude pricing page).
- Paid
- from $17 per month (billed annually; $20 monthly)
- Best at
- Letting you build repeatable behaviours, such as a tone or format, that Claude applies when you turn them on.
- The catch
- You supply and maintain the description of your style; the support article does not say Claude measures it from samples. That article is inconsistent on whether project instructions need a paid plan.
- web
- desktop
- mobile
A marketing platform whose Brand Voice feature "analyzes your content's tone of voice" and applies tone and formatting rules.
- Free
- A 7-day free trial.
- Paid
- from $59 per seat per month (Pro, billed yearly)
- Best at
- Keeping a team's writing on-brand, with style guides and knowledge assets.
- The catch
- Aimed at marketing teams: the Pro plan includes 2 Brand Voices per seat.
- web
- api
A humaniser that rewrites AI text with four preset tones or a custom voice, available with a free account.
- Free
- A free account unlocks the Humanizer agent with custom voice profiles (vendor page).
- Paid
- price not checked
- Best at
- Free voice options and wide app coverage, including Google Docs and Microsoft Office.
- The catch
- It rewrites existing AI text rather than drafting from your brief, and Grammarly says it is not intended to bypass AI detectors. Full functionality needs Grammarly Pro.
- web
- chrome
- ios
- android
- desktop
ScriptGrain
oursMeasures the rhythm, vocabulary, structure and habits in your own writing on 45 reference points, builds a voice profile and drafts new content in it, scoring each draft against it.
- Free
- Free: one voice profile, all 45 points, one draft, and connecting ChatGPT or Claude. No card needed.
- Paid
- from £12 per month (Writer; £115 a year)
- Best at
- Writing in YOUR measured voice, with a voice-match score on every draft and Voice Brain memory of what you have already covered.
- The catch
- The free plan gives one voice profile, one analysis and one draft; more drafts need a paid plan. Its homepage asks for 120 words or more of your own writing to start.
- web
- api
The same shortlist, as a table
| Thing | Free tier | Paid from | Platforms | The catch |
|---|---|---|---|---|
| ChatGPT custom instructions and memoryrel="nofollow noopener" | Custom instructions are on all plans (vendor help page); Memory is limited on Free per the pricing page. | not checked | web, desktop, ios, android | You describe your style yourself, within a limit: 1,500 characters on Free and Go, 5,000 on Plus, Pro, Business and Education. The help page does not say it measures your writing. |
| Claude instructions and skillsrel="nofollow noopener" | A free plan exists, with Pro at the price shown (Claude pricing page). | $17 per month (billed annually; $20 monthly) | web, desktop, mobile | You supply and maintain the description of your style; the support article does not say Claude measures it from samples. That article is inconsistent on whether project instructions need a paid plan. |
| Jasper Brand Voicerel="nofollow noopener" | A 7-day free trial. | $59 per seat per month (Pro, billed yearly) | web, api | Aimed at marketing teams: the Pro plan includes 2 Brand Voices per seat. |
| Grammarly Humanizer voice profilesrel="nofollow noopener" | A free account unlocks the Humanizer agent with custom voice profiles (vendor page). | not checked | web, chrome, ios, android, desktop | It rewrites existing AI text rather than drafting from your brief, and Grammarly says it is not intended to bypass AI detectors. Full functionality needs Grammarly Pro. |
| ScriptGrain ours | Free: one voice profile, all 45 points, one draft, and connecting ChatGPT or Claude. No card needed. | £12 per month (Writer; £115 a year) | web, api | The free plan gives one voice profile, one analysis and one draft; more drafts need a paid plan. Its homepage asks for 120 words or more of your own writing to start. |
How we checked
What we read, and what we haven't tested yet.
On 2 October 2026 we read the vendor pages listed under sources: OpenAI's custom instructions and Memory help pages and ChatGPT pricing page, Claude's personalisation help article and pricing page, Jasper's pricing page, Grammarly's humaniser page, and ScriptGrain's home and pricing pages. The old Claude styles help article returned a 404, so we describe only the instructions and skills it now documents. ChatGPT prices did not show on its pricing page. We didn't test any of these hands-on.
If none of these fit
The manual way.
The free way is to paste two or three samples of your own writing into a chatbot, ask it to describe your style, then save that description as custom instructions. ScriptGrain's own page says it measures the rhythm, vocabulary, structure and habits that make writing yours, which is what that manual description is trying to capture.