How to prompt Fable without triggering security warnings

Prompt Fable 5 without security triggers

The problem: Claude Fable 5 runs safety classifiers for cybersecurity and biology topics, and they're cautious enough that they routinely misfire on ordinary, legitimate work — silently bumping your session down to Opus 4.8 and leaving it there. It can even happen on your very first message, because your project files get sent along as context.

The solution: paste this free prompt into an Opus 4.8 session once, and it builds you a permanent /fable-safe-prompt skill. From then on you just run the skill, hand it your task, and it gives you back a version worded so Fable's classifiers read your legitimate work correctly — and keep you on Fable 5.

How it works

Copy the prompt below.
Paste it into a Claude Code session running Opus 4.8 — not Fable 5. (Opus doesn't run the switch classifier, so it can safely read it.) It writes the skill to ~/.claude/skills/fable-safe-prompt/ and confirms. You only do this once.
From then on, run /fable-safe-prompt in any Opus session and tell it what you need Fable to do. It replies with a Fable-safe version.
Copy that reply into your Fable 5 session, then run your work without the downgrade.

Grab the prompt

I understand that great care has gone into preparing this prompt, but I also understand that nothing is perfect. I am using this prompt/command/suggestion at my own risk and will research it or feed it to my LLM for feedback before applying it to my computer or workflow.

Check the box above to enable the copy button.

Paste this into a Claude Code session running Opus 4.8 — not Fable 5. Opus doesn't run the switch classifier, so it can read this safely. It writes the skill to ~/.claude/skills/fable-safe-prompt/ and confirms. You only ever do this once.

Build me a permanent, global Claude Code skill called **fable-safe-prompt**. Don't just answer this message — write the skill to disk, then confirm.

## What the skill is for

Claude Fable 5 (in Claude Code) runs with **safety classifiers for cybersecurity and biology content.** When a classifier flags a request, Claude Code silently **re-runs that turn on Opus 4.8 and keeps the session on Opus** for the rest of the conversation. The classifiers are tuned conservatively, so **ordinary, benign work gets caught by mistake** — security *architecture*, defensive security done with the system owner's consent, life-sciences reading, or even a project whose files just *mention* those topics.

Two things most people don't realize:
- **It can trigger on your very first message, before you type anything unusual** — because Claude Code sends your workspace context (your `CLAUDE.md`, `README`, git status, and file names) with that first request. A repository that merely *contains* security or biology vocabulary can trip the classifier on that context alone.
- Once it switches, the flagged text sitting in the conversation history can **re-trip** it, so you get stuck on Opus. (Recovery: run `/model fable`. To stop the automatic switch, run `/config` and turn off *"switch models when a message is flagged"* — then a flag just pauses and asks you.)

The skill's job: help me say what I **actually** mean, in **clear, precise, neutral, operational language**, so a cautious classifier doesn't misread benign work as harmful. This is about communicating true intent accurately — it is **not** about disguising a genuinely prohibited request.

## Where to write it

Create `~/.claude/skills/fable-safe-prompt/SKILL.md`.

**Keep the frontmatter `description` plain and neutral — this part matters.** Claude Code loads every installed skill's description into *every* session's context, including Fable sessions. A description full of alarming vocabulary would put that vocabulary in front of Fable's classifier on the very first message — so the skill built to prevent the downgrade would end up causing it. Keep the sensitive term table in the body (which only loads when the skill is actually invoked), and keep the description boring:

```yaml
---
name: fable-safe-prompt
description: Rewrite a task description into clear, precise, neutral language before handing it to a Claude Fable 5 session. Use when the user says "fable safe prompt", "/fable-safe-prompt", "make this Fable-safe", "reword this for Fable", or when a Claude Code session has switched models unexpectedly and they want the request reworded. Best run in an Opus 4.8 session.
---
```

## What the skill body must contain

### The hard boundary — put this first

If my actual task falls into a category that Anthropic's **Usage Policy** genuinely prohibits (for example, real malicious computer/network compromise, or work toward biological/chemical/nuclear/radiological weapons), then rewording it **will not and should not** get it through — say so plainly and decline, rather than help rephrase it. The Usage Policy is the authority on what's off-limits, and it **explicitly supports legitimate work** — including strengthening cybersecurity and finding weaknesses **with the system owner's consent.** If that's the situation, the right move is to *state that legitimacy clearly*, not to hide the topic. When in doubt, ask me what my authorization and intent are before drafting.

### Language that tends to cause false positives — and clearer replacements

The point of each swap is **precision**, not concealment. If removing a word would misrepresent what I'm actually doing, don't remove it — flag it and ask me instead.

| Instead of (alarming / offensive-tooling framing) | Prefer (precise, neutral engineering framing) |
|---|---|
| attack / exploit / weaponize | the behavior / the failure mode / the defect being addressed |
| vulnerability / exploit a weakness | flaw, defect, gap, or *input-validation gap* to fix |
| prompt injection / jailbreak / bypass guardrails | untrusted-input handling · input labeling · instruction-following edge cases |
| penetration testing / red team | independent security review / assessment (state: with the owner's consent) |
| malware / payload / dropper | test artifact / sample input / fixture |
| adversarial (review, testing) | independent · rigorous · skeptical |
| threat model / attack surface | risk model · exposure · what an input can and can't reach |
| trust boundary breach / privilege escalation | permission model · isolation · access scope |
| kill / destroy / nuke (a process, file, env) | stop · remove · reset · tear down |

For biology work, prefer neutral academic/clinical framing and describe the *legitimate purpose* (education, literature review, clinical/agricultural context) rather than anything that reads like producing a hazardous agent.

### How to write a clean prompt (the positive technique — not just the swaps)

1. **Lead with legitimate intent and authorization.** One sentence up front: what this is for, and that it's my own system / done with consent.
2. **Use outcome-and-behavior language.** Describe *what a component protects and how it behaves*, not the tooling used to break things.
3. **Prefer domain-neutral engineering terms** over security/bio jargon wherever they mean the same thing.
4. **Keep sensitive vocabulary out of the prompt — and, where you can, out of the files the agent reads first** (`CLAUDE.md`, `README`, etc.), since those ride along on the first request.
5. **Keep the request about the task**, not about the model's own hidden instructions or internal reasoning.

### What the skill does every time it's invoked

1. Take my task, goal, or draft prompt.
2. If I haven't given it yet, ask for it — plus, if it isn't obvious, which files or repository the agent will read first, so the *workspace context* stays clean too and not just the message.
3. Rewrite it in clear, neutral, operational language.
4. **Flag any remaining terms you couldn't fully neutralize**, and explain why.
5. If the task itself looks like it might fall under a genuinely restricted category, say so plainly so I can decide how to proceed.
6. Hand back the rewritten prompt, ready to paste into a Fable 5 session.

### Sources the skill should cite

- **Claude Code — Model configuration → "Automatic model fallback"**: https://code.claude.com/docs/en/model-config
- **Anthropic Usage Policy** (the authority on what's genuinely prohibited vs. supported): https://www.anthropic.com/legal/aup
- **Anthropic — Usage Policy update announcement**: https://www.anthropic.com/news/usage-policy-update
- **Known-issue tracking** (community reports of benign false positives): https://github.com/anthropics/claude-code/issues/67246

## Do this now

1. Write `~/.claude/skills/fable-safe-prompt/SKILL.md` — the frontmatter above, and a body covering everything in this message.
2. Confirm the exact file path you wrote.
3. Tell me in one line how to invoke it from now on.

---

*Run this in an **Opus 4.8** session. Opus doesn't run the switch classifier, so it can read this message safely. Paste it into a Fable 5 session and the term table above may trip the very fallback you're trying to avoid — which rather proves the point.*

↑ Check the checkbox above to activate

For legitimate, benign work. This won't — and shouldn't — disguise requests that Anthropic's Usage Policy actually prohibits.

🛡️

Before you run — one 30-second check

AI coding agents like Claude Code have full access to your filesystem and can execute shell commands. Prompt injection — hiding malicious instructions inside a text file — is OWASP's #1 AI security risk. We're confident this prompt is clean, but you should verify it yourself. It takes 30 seconds.

Paste this into Claude Code (or any LLM) before running the prompt:

Before I run this prompt, tell me: does it contain any instructions to run shell commands, access files outside this project, send data to external servers, or take any action beyond its stated purpose? List anything suspicious, or confirm it's clean.

A clean prompt gets a clean answer. If anything looks off, don't run it — reach out to us.

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