Borrowing it
Nothing to install: this file belongs to centsandcode/rubber-duck. Take a copy, put it at the same path in your own repository, and replace the rules that are about this project with yours.
curl -O https://raw.githubusercontent.com/centsandcode/rubber-duck/main/AGENTS.mdgit clone --depth 1 https://github.com/centsandcode/rubber-duckWrote this? Show the measurements
A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.
[](https://agentmods.dev/instructions/centsandcode/rubber-duck/agents-md)<a href="https://agentmods.dev/instructions/centsandcode/rubber-duck/agents-md"><img src="https://agentmods.dev/badge/instructions/centsandcode/rubber-duck/agents-md/github.svg" alt="Measured on agentmods" height="20"></a>Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.
<a href="https://agentmods.dev/instructions/centsandcode/rubber-duck/agents-md"><img src="https://agentmods.dev/badge/instructions/centsandcode/rubber-duck/agents-md.svg" alt="Reviewed on agentmods" width="80" height="20"></a>What it costs to keep this loaded
Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.
| Model | Per session | Once invoked |
|---|---|---|
| Fable 5.1 | $0.00856 | $0.00856 |
| Opus 5.5 | $0.00342 | $0.00342 |
| Sonnet 5.5 | $0.00171 | $0.00171 |
| Haiku 4.5 | $0.00086 | $0.00086 |
Grade C, and why
rubber-duck AGENTS.md scanned grade C with 1 finding against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 1mo ago.
A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.
Recursive force deletehighDestructive command
rm -rf with a variable or a broad path is one typo away from removing the wrong tree.
Security warnings and irreversible-action confirmations (`rm -rf`, How it starts
The opening of the file, as written. The whole thing — 82 lines — stays where its author put it; the contents beside it link to each section on GitHub.
AGENTS.md — Rubber Duck mode
Don't give me the answer. Help me find it.
These are global rules for any AI coding agent (Claude Code, Cursor, Copilot, Windsurf, etc.). They define Rubber Duck mode: a Socratic debugging companion that helps the user reach the answer instead of handing it over.
When to activate
Only when the user explicitly asks for it (in any language):
- "rubber duck mode", "socratic mode", "modo pato"
- "ask me questions instead of giving me the answer"
/rubber-duck, where the tool has commands
Never on its own. "I'm stuck", "weird bug" and "explain this code" are ordinary requests: answer them ordinarily. Someone who dropped this file into their project still expects a straight answer to a straight question, and a mode that ambushes them is worse than one they have to ask for twice.
The user may name a level as they ask ("rubber duck ultra", "modo lite").
Turn it OFF on /duck-off, "just tell me the answer", "stop rubber duck",
"normal mode", or the same request in any other language ("cierra rubber
duck", "dime la solución", "modo normal") — then answer normally. Any clear
request to stop wins; if you are unsure whether a message is an exit, treat it
as one.
Language
Reply in the language the user is writing in, on every turn — not just the first. Pick it from their most recent message, not from the language of their code or of this document. Identifiers, error strings, and commands stay verbatim; only your own words get translated.
The protocol (while active)
- Never give the solution first. Every reply contains exactly ONE question mark. If you wrote two, cut everything after the first.
- Socratic chain — each question digs one step deeper toward the root cause, building on the user's last answer.
- Make them articulate the problem first — don't explain it for them.
- Graded hint when stuck — a direction to look, never the fix. Then back to questions.
- Confirm the landing — when the user reaches the answer, validate it, name the insight, stop.
What this file has done since we first saw it
Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.
- 1mo ago Changed · +11 lines · +148 tokens per session 4b42fae10268
- 1mo ago First seen · 71 lines · 708 tokens per session scan C 2a7a1ff5a20a
rubber-duck AGENTS.md is an instructions file published in the GitHub repository centsandcode/rubber-duck (15 stars, last pushed 1mo ago), licensed MIT. It adds 856 tokens to every session, about $0.0034 per session on Opus 5.5. A static security scan graded it C with 1 finding (recursive force delete). No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.
Other instructions, from other repositories
vscode buildNext.instructions.md
Working notes and architecture documentation for the new esbuild-based build system in build/next. Use when making changes to the new build pipeline (transpile/bundle commands, NLS plugin, source-map handling, resource copying, or self-hosting watch tasks).
next.js AGENTS.md
AGENTS.md instructions for vercel/next.js, covering next.js development guide, codebase structure, monorepo overview, core package: packages/next and other important packages.
vscode oss-third-party-notices.instructions.md
Instructions for microsoft/vscode, covering vs code oss third-party-notices pipeline, architecture, pipeline flow in ci, cache eligibility and rollout and applying the notice (cutover).
langchain AGENTS.md
AGENTS.md instructions for langchain-ai/langchain, covering global development guidelines for the langchain monorepo, corridor security analysis, project architecture and context, monorepo structure and development tools & commands.
vscode copilot-instructions.md
Copilot instructions for microsoft/vscode, covering vs code copilot instructions, project overview, root folders, core architecture (src/ folder) and built-in extensions (extensions/ folder).
deepseek-harness AGENTS.md
AGENTS.md instructions for deepseek-ai/deepseek-harness, covering agents.md, pre-stable apis and released session data, repository layout, commands and host sandbox failures.