System Prompts Leaks is a collection of captured system instructions used to guide AI chatbots and coding agents before they receive user messages. It serves researchers and developers studying how different AI assistants are directed.
Getting it into your agent
One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.
npx skills add asgeirtj/system_prompts_leaks --skill cookie-debugginggit clone --depth 1 https://github.com/asgeirtj/system_prompts_leaksWrote 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/skills/asgeirtj/system_prompts_leaks/cookie-debugging)<a href="https://agentmods.dev/skills/asgeirtj/system_prompts_leaks/cookie-debugging"><img src="https://agentmods.dev/badge/skills/asgeirtj/system_prompts_leaks/cookie-debugging/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/skills/asgeirtj/system_prompts_leaks/cookie-debugging"><img src="https://agentmods.dev/badge/skills/asgeirtj/system_prompts_leaks/cookie-debugging.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 | $0.00071 | $0.02176 |
| Opus 5.5 | $0.00028 | $0.00870 |
| Sonnet 5.5 | $0.00014 | $0.00435 |
| Haiku 4.5 | $0.00007 | $0.00218 |
Grade A, and why
cookie-debugging scanned grade A 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 today.
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.
Makes network callslowCapability
Not a fault in itself. Listed so you know the mod talks to something, and to what.
- Call `evaluate_script` with `() => fetch(window.location.href)` Copies of this mod
3 near-identical copies found in the catalogue:
- cookie-debugging — 100% identical, 2 lines differ
- cookie-debugging — 100% identical, 15 lines differ
- cookie-debugging — 97% identical, 17 lines differ
How it starts
The opening of the file, as written. The whole thing — 150 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Core Concepts
HttpOnly vs Client-Side Storage
Cookies marked HttpOnly cannot be accessed or modified by client-side JavaScript (cookieStore or document.cookie). However, the browser automatically attaches active HttpOnly cookies to outgoing HTTP request headers (Cookie).
- To inspect current
HttpOnlyvalues: Look at theCookierequest header of any outgoing HTTP request viaget_network_request. - To inspect how cookies were created or configured: Look at the
Set-Cookieresponse header of login/auth responses. - To inspect non-
HttpOnlycookies: Useevaluate_scriptwith the moderncookieStoreAPI (async () => await cookieStore.getAll()).
Session Strategy: Live Tab vs Isolated Context
Choose the right session environment to avoid state contamination (e.g., residual analytics or auth tokens):
| Strategy | When to Use | Setup / Teardown |
|---|---|---|
| Live Tab (Active Page) | Diagnosing an active user session, live 401/403 error, or current state. | Operates directly on the currently selected page. |
Clean-Slate (isolatedContext) |
Testing cookie consent banners, first-time visits, or zero-cookie guarantees. | Call new_page with a unique isolatedContext (e.g. "consent-audit-1"). When finished, call close_page. |
Client-Side Capabilities & Limitations
| Action | Client JavaScript (cookieStore / document.cookie) |
DevTools Network & Context Tools |
|---|---|---|
| Read Non-HttpOnly | ✅ async () => await cookieStore.getAll() |
✅ get_network_request (Request Cookie) |
| Read HttpOnly | ❌ Blocked by browser security | ✅ get_network_request (Request Cookie) |
Inspect Attributes (Domain, Path, SameSite, Expires) |
✅ async () => await cookieStore.getAll() |
✅ get_network_request (Response Set-Cookie) |
| Modify / Delete Non-HttpOnly | ✅ async () => await cookieStore.set(...) |
N/A |
| Modify / Delete HttpOnly | ❌ Silent failure in JavaScript | ✅ Use new_page(isolatedContext: ...) for clean state |
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.
- today First seen · 150 lines · 71 tokens per session scan A 8add4b0de39d
cookie-debugging is a skill published in the GitHub repository asgeirtj/system_prompts_leaks (70,425 stars, last pushed today), licensed CC0-1.0. It adds 71 tokens to every session and 2,176 once invoked, about $0.0003 per session on Opus 5.5. A static security scan graded it A with 1 finding (makes network calls). No closer match exists in the catalogue, so it is treated as the original; first seen 2026-10-30.
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