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 minghinmatthewlam/agent-guards --skill principle-separate-before-serializing-shared-stategit clone --depth 1 https://github.com/minghinmatthewlam/agent-guardsWrote 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/minghinmatthewlam/agent-guards/principle-separate-before-serializing-shared-state)<a href="https://agentmods.dev/skills/minghinmatthewlam/agent-guards/principle-separate-before-serializing-shared-state"><img src="https://agentmods.dev/badge/skills/minghinmatthewlam/agent-guards/principle-separate-before-serializing-shared-state/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/minghinmatthewlam/agent-guards/principle-separate-before-serializing-shared-state"><img src="https://agentmods.dev/badge/skills/minghinmatthewlam/agent-guards/principle-separate-before-serializing-shared-state.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 | $0.00050 | $0.00326 |
| Opus 5.5 | $0.00020 | $0.00130 |
| Sonnet 5.5 | $0.00010 | $0.00065 |
| Haiku 4.5 | $0.00005 | $0.00033 |
Grade A, and why
principle-separate-before-serializing-shared-state 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.
This is a copy
88% identical to principle-separate-before-serializing-shared-state — 0 lines differ, which has more behind it and is treated as the original. This page carries a canonical link to it rather than competing with it.
What it actually says
Separate Before Serializing Shared State
When concurrent actors might share mutable state, first ask whether they need the same mutable object. If not, eliminate the sharing. When sharing is real, enforce serialization structurally: lockfiles, sequential phases, exclusive ownership. Instructions and conventions are not concurrency control.
Why: Concurrent writes to shared state create race conditions that are intermittent, hard to reproduce, and expensive to debug.
Pattern:
- Identify shared mutable state (files both read and write, branches both push to, APIs both define and consume).
- Default: eliminate the shared write target. Ask: do these actors need one canonical object, or are they publishing independent facts? Give each actor its own owned file, key, branch, or state directory, and merge only at the read/reporting boundary. Two workers writing their own
lastXfield into onestate.jsonis still shared mutation.indexer-state.json+metrics-state.jsonis not. - Only when one shared write target is a real invariant, serialize access structurally (lockfiles, sequential phases, single-writer actor, or atomic compare-and-swap). Treat "we need a lock" as a design smell to check, not as the default answer.
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 · 17 lines · 50 tokens per session scan A dd432081bc56
principle-separate-before-serializing-shared-state is a skill published in the GitHub repository minghinmatthewlam/agent-guards (47 stars, last pushed 2d ago), licensed MIT. It adds 50 tokens to every session and 326 once invoked, about $0.0002 per session on Opus 5.5. A static security scan graded it A with 0 findings. It is 88% identical to principle-separate-before-serializing-shared-state, differing in 0 lines, and is treated as a copy.
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