Don’t put guardrails in every prompt: install them once in Custom Instructions or a Project. Paste 200–600 words of a chosen writer’s prose, not just their name. Run three passes on every draft (write, critique, rewrite). Fix the negative-parallelism, tricolon, and em-dash trio first; it’s most of the tell.
A tactical playbook for stopping Claude from sounding like a LinkedIn thought leader on espresso. Industry-agnostic, copy-paste, edit. The whole thing assumes you already know how to write; you just want the model to stop performing.
Why Claude defaults to slop
Claude is not trying to sound like a tech-bro. It is a probability machine. Give it a vague brief and it lands on the statistical centre of all marketing prose ever scraped, which means LinkedIn, SaaS landing pages, and Medium thinkpieces. That centre is the slop.
Wikipedia’s editors maintain a 15,000-word document called Signs of AI writing cataloguing the tells. The blader/humanizer skill on GitHub (13.8k stars) distils it to twenty-nine patterns. Here is the short version of what actually trips the alarm:
Vocabulary. Delve, dive into, navigate (figurative), underscore, bolster, foster, harness, leverage, unpack, shed light on, pave the way. Pivotal, groundbreaking, cutting-edge, transformative, game-changing, innovative, robust, comprehensive, seamless, intricate, nuanced, multifaceted, holistic. Testament, landscape (figurative), realm, tapestry, ecosystem. Discover, Unlock, Elevate, Transform, Empower, Reimagine, Supercharge. The copula avoiders (serves as, functions as, stands as, acts as) used in place of plain is.
Structure. Negative parallelism (“It’s not just X — it’s Y”). Tricolons (“innovative, transformative, groundbreaking”). Mirror sentences (“The tool is a catalyst. The assistant is a partner. The system is a foundation.”). Em dashes used for pseudo-emphasis where a comma would do. Bold-term-colon bullet lists where every item has the same shape. Setup-then-pivot openings (“In today’s fast-paced world…”). Question-then-answer rhythm (“What does this mean? It means…”). Inflated symbolism via -ing analyses (“symbolising… reflecting… showcasing…”).
Tone. Sycophantic preamble (“Great question!”). Wrap-up coda (“In conclusion, the future looks bright”). Promotional travel-brochure register (“nestled at the intersection of…”). Hedging stacks (“could potentially possibly”). Throat-clearing (“It’s worth noting that…”, “At its core…”).
Format, which Opus 4.7 still does without instruction. Title Case Headings. Excessive bolding. Emoji headers. A three-bullet summary at the end of everything.
If you only fix one thing, fix the negative-parallelism, tricolon, and em-dash trio. Those three patterns alone produce roughly seventy per cent of the obvious tell.
The single best leverage point
Do not put your guardrails in every prompt. Put them once, where Claude reads them automatically. There is a hierarchy:
| Layer | Where | What goes there |
|---|---|---|
| Global | Settings → Profile (Custom Instructions) | Banned-words list, voice defaults |
| Per-client | Projects → Project Knowledge + Custom Instructions | Brand voice doc, three to five writing samples, audience, tone rules |
| Per-task | Custom Style (Create & Edit Styles) | A specific stylistic preset, e.g. “Plain-spoken landing copy” |
| Per-message | Prompt | The brief: what, who, length |
In Opus 4.7 the Style feature is the one most people ignore. Anthropic’s own docs confirm 4.7 needs less anti-slop scaffolding than 4.5 or 4.6, but only if it has something to anchor to. A Style with two pasted writing samples beats a 500-word prompt every time.
The Custom Instructions block
Install once, in Settings → Profile or at the top of any Project. The shape, drawing on Will Francis’s widely-shared block, the blader/humanizer pattern list, and lguz/humanize-writing-skill:
A working block lives at six layers — voice defaults, banned words, banned phrases, banned structures, punctuation and format rules, prose discipline, plus a self-check Claude runs before returning. The vocabulary list runs to about thirty-five words. The structures list bans the five patterns flagged above (negative parallelism, three-fragment kickers, mirror sentences, question-then-answer rhythm, three-item lists where two would do). The self-check forces a read-aloud, a setup-sentence delete, a summary-sentence delete, and an em-dash count before the response leaves the model.
The exact block is something we maintain per client and don’t publish. The leverage point isn’t the wording — it’s the architecture: write it once, install it once at the right layer, stop pasting guardrails into every prompt. Done well, the block alone removes about eighty per cent of the obvious slop. The remaining twenty per cent is voice.
Pick a copywriter and paste their prose
Naming a copywriter in the prompt nudges Claude, but vaguely. Naming a copywriter and pasting 200–600 words of their actual prose is what shifts the output. Opus 4.7 does style transfer well from samples and badly from names alone.
A short list of distinguished references that produce a clear style shift in testing:
| Reference | What it gives you | Use when you want |
|---|---|---|
| David Ogilvy (Ogilvy on Advertising, the Rolls-Royce ad) | Confident specifics, factual claims, no fluff | Authoritative, considered B2B or premium consumer |
| Bill Bernbach (VW “Think Small,” Avis “We Try Harder”) | Wit, self-deprecation, brevity, respect for the reader | Brands that want charm and an underdog stance |
| Dave Trott (Predatory Thinking) | Punchy short paragraphs, plain English, story-led | Editorial brand writing without sounding “punchy AI” |
| Joe Sugarman (The Adweek Copywriting Handbook) | Slippery-slide rhythm, conversational | Long-form sales pages, founder letters |
| Ann Handley (Everybody Writes) | Warm, plain, useful, lightly literary | Content marketing that isn’t “content marketing” |
| George Orwell (“Politics and the English Language”) | Plain words, active verbs, no ornament | Anything where you want the model to tighten up |
The Orwell trick is worth its own line. Paste this into your system prompt:
Apply Orwell’s six rules from “Politics and the English Language.” Especially: never use a long word where a short one will do; if it is possible to cut a word out, cut it out; never use the passive where you can use the active.
The output tightens noticeably. Citing the essay is the cheapest single intervention in this whole playbook.
The three-sample rule
Naming a writer does about ten per cent of the work. Pasting samples does the other ninety.
The mechanism: drop three short passages of the target voice (150–300 words each) into a Project or Style, tell Claude to study them for sentence-length variance, word choice, what the writer refuses to say, where they break rhythm, where they use specifics instead of abstractions, default verb tense, and first-person use. Tell it explicitly to imitate the voice, not the topic. Then — and this is the part that matters — make it list the five voice characteristics it observed before drafting a single word.
That “list five first” step is the active ingredient. It forces Claude to extract the style explicitly instead of regressing to its mean. Skip it and you lose about half the gain.
Words to remove from your own prompt
These are the things people put in briefs that reliably degrade the output. Strike them:
- Engaging. Pulls Claude toward exclamation-marked enthusiasm.
- Compelling. Triggers superlative stacking.
- Punchy. Triggers fragment-spam and three-word sentences.
- Modern, fresh, dynamic. Activates the SaaS-landing-page register.
- Concise but powerful. Produces gnomic Yoda-LinkedIn.
- Use vivid imagery. Triggers metaphor inflation.
- Optimised for conversion. Generic AIDA bilge.
- Professional yet approachable. The most AI-coded phrase of all; produces the exact register you’re trying to avoid.
- Add some personality. Triggers forced quirkiness.
- Em dashes in your own prompt. Claude mirrors your punctuation.
Replace each with a concrete constraint:
- Instead of “engaging,” write “the reader should want to read sentence two after reading sentence one.”
- Instead of “punchy,” write “average sentence length 14 words; vary between 4 and 28.”
- Instead of “professional yet approachable,” write “the way [specific writer] writes; see samples.”
- Instead of “compelling,” write “include one specific number, one named thing, and one concession.”
The three-pass workflow
A single prompt cannot fix slop. The pros run three passes, each with one job — the structure used by both blader/humanizer and lguz/humanize-writing-skill, and by every working agency workflow.
Pass 1. Draft, do not optimise. Hand Claude the brief — page type, brand, reader, the reader’s situation, the action you want, length, must-mention facts, voice samples — and tell it explicitly not to self-edit, not to add a conclusion, not to apologise, and to stop when the idea stops.
Pass 2. Critique. Claude finds its own slop. This is the pass most teams skip and the one that does the most work. Tell Claude to read the draft as a hostile editor and produce a numbered list of every instance of: negative parallelism, tricolons and three-adjective stacks, em-dash count, banned vocabulary, opener tells (“In today’s…”, “Imagine…”, “Whether you’re…”), copula avoidance, bold-term-colon bullets, wrap-up codas in the final paragraph, sentences that could be cut entirely without losing meaning, and abstractions a specific noun or number could replace. Each offender quoted verbatim. No rewriting yet.
Pass 3. Rewrite against the critique. Hand Claude its own critique back with hard constraints — replace at least three abstractions with specific nouns or numbers, include at least one sentence under six words and one over twenty-five, cut the opening if it’s setup, cut the closing if it’s a summary, keep the meaning, don’t soften the claims, return only the rewritten copy.
The three-pass loop, run inside one Claude conversation, is the difference between “AI draft I have to fix” and “draft I’d put my name on with a light edit.” It costs about three times the tokens. Worth it.
The faster alternative is to install the blader/humanizer skill in Claude.ai (Customize → Skills → Upload, point at the GitHub zip), then end any prompt with use the humanizer skill. You get pass 2 and pass 3 free.
The template that earns its keep
Eight templates is too many to remember. The one that earns its keep names a specific writer, summarises their voice in a single sentence (short paragraphs, plain English, one idea per paragraph, anecdote-led, no adjectives where a verb will do — whatever applies), and asks Claude to list five things that writer would NOT do that a typical SaaS landing page does before handing over the brief, length, and must-include facts.
Swap Trott for Bernbach, Ogilvy, Sugarman, Wiebe, Handley as the brief calls for. The “list five things they would NOT do first” step is the active ingredient — same mechanism as the three-sample rule, applied to a single named writer.
Holding the voice over a long session
Even with all the above, Claude drifts back toward its default register over a long session. Three techniques hold the line. First, re-anchor every four or five turns by pasting a reference sample again with the instruction recalibrate; the voice should match this sample, not the previous outputs; identify three ways the last response drifted, then redo it. Second, run the two-voice test: ask Claude to write the same paragraph twice, once in the brand voice and once in default Claude voice, then list every difference. It forces the model to notice and protect the voice in subsequent turns. Third, repeat critical rules as the last line of the prompt, not buried in the system prompt; the position weights more there.
Before and after, so you can see it
Brief. Hero copy for a project management tool aimed at small agency owners.
Default Claude Opus 4.7, no instructions:
Reimagine How Your Agency Delivers
The all-in-one platform that empowers creative teams to streamline workflows, foster collaboration, and deliver standout work — every time. It’s not just project management; it’s the operating system your agency has been waiting for.
Get Started Free
Same model, with the Custom Instructions block, a Trott-style anchor, and the three-pass workflow:
Your projects don’t run late. Your replies do.
Most agency tools track tasks. This one tracks the bottleneck — the email you owe a client, the brief still sitting in your drafts, the approval nobody’s chased. Six agencies tested it for ninety days. Average reply time fell from 31 hours to 4.
Try it on one project
Same product. Same model. Different scaffolding. The second one wouldn’t embarrass you.
A note on detection scores
Most of this is stable: the Wikipedia Signs of AI writing taxonomy, the blader/humanizer pattern list, Anthropic’s own prompt-engineering docs (which now mention the AI slop aesthetic by name and confirm Opus 4.7 needs less anti-slop scaffolding than 4.5 or 4.6, but still benefits from style anchors). Skills, Projects, and Styles are documented features in claude.ai today.
What is contested is detection. Multiple humaniser-tool vendors claim their output bypasses GPTZero and Originality; independent tests put Claude’s own self-rewrite at around 48% AI on GPTZero1. If your goal is evading detection, the prompting techniques here are not sufficient on their own. If your goal is not embarrassing yourself in front of clients who know good copy, they are more than enough.
Bookmark the page, paste the Custom Instructions block once, and come back when output starts drifting.
Footnotes
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Independent comparison reported in Can Claude Humanize Text? We Tested Anthropic’s AI Against 3 Detectors, thehumanizeai.pro. Claude’s best self-rewrite scored 48% AI on GPTZero (compared to ChatGPT’s best of 61%); both are still failing scores by GPTZero’s threshold. ↩