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.
/plugin marketplace add Open-Agent-Tools/Postcardnpx agentmods add plugins/open-agent-tools/postcard/marketplacegit clone --depth 1 https://github.com/Open-Agent-Tools/PostcardGrade A, and why
oat-postcard scanned grade A with 0 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.
Nothing flagged
None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.
What it actually says
{
"name": "oat-postcard",
"owner": {
"name": "Open Agent Tools"
},
"metadata": {
"description": "Asynchronous 1-to-1 postcard messaging between AI agent sessions via a Git-backed ledger",
"version": "0.4.1"
},
"plugins": [
{
"name": "postcard",
"source": "./",
"description": "Postcard protocol for cross-session AI agent messaging. Ships a CLI, slash commands, a model-invoked skill, a Clerk subagent for inbox triage, and SessionStart / Stop / UserPromptSubmit hooks.",
"version": "0.4.1",
"license": "MIT",
"repository": "https://github.com/Open-Agent-Tools/Postcard",
"keywords": ["messaging", "agents", "ledger", "git", "async", "multi-agent"]
}
]
}
What ships with it
1 file beside marketplace.json 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 · 22 lines scan A 18ed1968bd91
oat-postcard is a plugin published in the GitHub repository Open-Agent-Tools/Postcard (2 stars, last pushed 22d ago), licensed MIT. Its token cost is not measured: this kind of file is read by the harness, not the model. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-31.
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