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 instructions/goccy/sheena/agents-mdgit clone --depth 1 https://github.com/goccy/sheenaWhat 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 | $0.01152 | $0.01152 |
| Opus 5 | $0.00576 | $0.00576 |
| Sonnet 5 | $0.00230 | $0.00230 |
| Haiku 4.5 | $0.00115 | $0.00115 |
Grade A, and why
sheena AGENTS.md 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 3d 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.
How it starts
The opening of the file, as written. The whole thing — 95 lines — stays where its author put it; the contents beside it link to each section on GitHub.
AGENTS.md
Guidance for AI agents and human contributors working in this repository. These
rules are mandatory for every change. (A Claude-specific superset lives in
CLAUDE.md; this file is the tool-neutral version.)
What Sheena is
A lightweight, in-process sandbox for safely executing the tool calls an AI
agent requests, on the same host as the agent. See README.md for the API and
DESIGN.md for the full design.
Go version & idioms
- Target Go 1.25.0. Any feature up to and including Go 1.25 may be used
(generics,
os.Root,io/fs.ReadLinkFS, range-over-func, etc.). - Prefer modern idioms. Use
any, neverinterface{}. Use generics where they remove duplication or improve type safety. - Keep
go.mod'sgo 1.25.0directive and the golangci-lint config in sync.
Testing & coverage
- Every package MUST maintain ≥90% statement coverage. Add tests until the bar is met; never lower it.
make test(go test -race ./..., with the wasm interpreters run separately without-race) andmake cover(per-package ≥90% gate) MUST pass.- Access-control behavior is documented and asserted with example tests
(
Example…+// Output:) — path traversal blocked, network denied by default, overlay never writes to the host. - Keep the dedicated suites: security/threat-model (
security_test.go), escape attempts (traversal, symlink escape, SSRF, redirect, output/command/memory caps, timeout), and the differential golden tests that check commands against real coreutils (internal/difftest).
Benchmarks
Sheena claims to be lightweight; that claim stays measured. Keep Benchmark…
for sandbox construction/mass startup (report allocs/op and B/op), per-call
ExecBash overhead, and parallel throughput (b.RunParallel). Run with
make bench; compare with benchstat when touching hot paths and do not
regress startup or allocations without a stated reason.
Linting
golangci-lint MUST pass with zero issues (make lint). Fix the underlying
issue rather than disabling a linter or adding a nolint directive; if a
suppression is truly warranted, justify it in the diff.
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.
- 3d ago First seen · 95 lines · 1,152 tokens per session scan A 096327e73e42
sheena AGENTS.md is an instructions file published in the GitHub repository goccy/sheena (22 stars, last pushed 1mo ago), licensed MIT. It adds 1,152 tokens to every session, about $0.0058 per session on Opus 5. 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 2026-08-30.
Other instructions, from other repositories
awesome-go AGENTS.md
AGENTS.md instructions for avelino/awesome-go, covering awesome-go · llm contribution guide, project snapshot, when modifying the awesome list, coding guidelines and testing & validation.
OpenSandbox CLAUDE.md
Claude Code instructions for opensandbox-group/OpenSandbox: See AGENTS.md for all rules, routing, and conventions.
agent-sandbox AGENTS.md
Instructions for kubernetes-sigs/agent-sandbox, covering agents.md, project summary, repository layout, agent skills and build, test, lint.
agent-sandbox copilot-instructions.md
Instructions for kubernetes-sigs/agent-sandbox: Project Context & Architecture: Refer to AGENTS.md for full project background, module layout, toolchain versions, and core conventions.
SmolVM AGENTS.md
Instructions for CelestoAI/SmolVM, covering smolvm context, 🚀 project overview, 🧪 development, key commands and release checklist.
ironcurtain CLAUDE.md
Instructions for provos/ironcurtain, covering claude.md, general workflow, git & worktrees, git workflow and platform considerations.