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 agentmods add skills/mvanhorn/agentcookie/skillnpx skills add mvanhorn/agentcookie --skill skillgit clone --depth 1 https://github.com/mvanhorn/agentcookieWhat 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 | $0.00063 | $0.02147 |
| Opus 5 | $0.00032 | $0.01073 |
| Sonnet 5 | $0.00013 | $0.00429 |
| Haiku 4.5 | $0.00006 | $0.00215 |
Grade B, and why
agentcookie-install scanned grade B with 2 findings 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 2d 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.
Asks for rootmediumPrivilege escalation
A mod that escalates privileges can change anything on the machine, not only the project.
sudo mv agentcookie /usr/local/bin/ Makes network callslowCapability
Not a fault in itself. Listed so you know the mod talks to something, and to what.
curl -LO https://github.com/mvanhorn/agentcookie/releases/download/v1.0.0/agentcookie_1.0.0_darwin_arm64.tar.gz How it starts
The opening of the file, as written. The whole thing — 240 lines — stays where its author put it; the contents beside it link to each section on GitHub.
agentcookie install
You are helping the user install agentcookie on two machines that are both on the same Tailscale tailnet, then pair them, so that the sink's Chrome stays continuously in sync with the source's Chrome.
After install, the user does not touch agentcookie again. The source watches Chrome via fsnotify and pushes every cookie change to the sink within seconds. On Linux, the sink injects cookies via CDP into an already-running Chrome. On macOS, a LaunchAgent keeps the daemon running across reboots.
Inputs you need
- Which machine is the source (the Mac the user logs into Chrome on, usually their laptop).
- Which machine is the sink (where AI agents act - a Linux VM like Grok Bot, or a second Mac).
- Tailscale is up on both.
- On Linux: Chrome is running with
--remote-debugging-port=9223(or another port).
If any of these are missing, stop and ask.
Flow: Mac source to Linux sink (featured path)
Step 0: detect the lay of the land
Run on the current machine:
uname -s # Darwin = macOS, Linux = Linux
tailscale status 2>&1 | head -20
From the Tailscale status output, identify which host is the Mac and which is the Linux box.
Step 1: confirm source vs sink with the user
Use the platform's blocking question primitive. Phrase it concretely:
I see you're on
<current-hostname>. Looks like<other-hostname>(Tailscale IP100.x.y.z) is your other machine. Should I install agentcookie with<current-hostname>as the source (your logged-in Chrome) and<other-hostname>as the sink (where your agents run)?
Confirm before proceeding. If wrong, ask which is which.
Step 2: install on the Mac source
Install the binary if missing:
# Download from GitHub Releases
curl -LO https://github.com/mvanhorn/agentcookie/releases/download/v1.0.0/agentcookie_1.0.0_darwin_arm64.tar.gz
tar -xzf agentcookie_1.0.0_darwin_arm64.tar.gz
sudo mv agentcookie /usr/local/bin/
Or build from source:
go install github.com/mvanhorn/agentcookie/cmd/[email protected]
What ships with it
1 file beside SKILL.md in the same directory: the scripts, references and assets a skill reads on demand. Not counted in the per-session cost; read them before you install if any of them is executable.
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.
- 2d ago First seen · 240 lines · 63 tokens per session scan B bad7392e5498
agentcookie-install is a skill published in the GitHub repository mvanhorn/agentcookie (808 stars, last pushed 8d ago), licensed MIT. It adds 63 tokens to every session and 2,147 once invoked, about $0.0003 per session on Opus 5. A static security scan graded it B with 2 findings (asks for root, makes network calls). No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.
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