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/ericlitman/open-pstack/principle-guard-the-context-windownpx skills add ericlitman/open-pstack --skill principle-guard-the-context-windowgit clone --depth 1 https://github.com/ericlitman/open-pstackWrote 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/ericlitman/open-pstack/principle-guard-the-context-window)<a href="https://agentmods.dev/skills/ericlitman/open-pstack/principle-guard-the-context-window"><img src="https://agentmods.dev/badge/skills/ericlitman/open-pstack/principle-guard-the-context-window.svg" alt="Measured on agentmods" 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 | $0.00046 | $0.00242 |
| Opus 5 | $0.00023 | $0.00121 |
| Sonnet 5 | $0.00009 | $0.00048 |
| Haiku 4.5 | $0.00005 | $0.00024 |
Grade A, and why
principle-guard-the-context-window 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 5d 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
92% identical to principle-guard-the-context-window — 6 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
Guard the Context Window
The context window is finite and non-renewable within a session. Every token that enters should earn its place.
Why: Context overflow degrades reasoning quality, creates compression artifacts, and halts progress. Unlike compute or time, context spent inside a session cannot be reclaimed.
Pattern:
- Isolate large payloads. Route verbose outputs, screenshots, and large documents to subagents. The main context gets summaries, not raw data.
- Don't read what you won't use. Read selectively based on relevance. If a file isn't needed for the current task, skip it.
- Keep frequently used content inline. Templates and references used on every invocation belong in the skill file, not in separate files that cost a read each time.
- Size phases and cap scope. Limit files per phase, set turn budgets, account for mechanism costs.
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.
- 5d ago First seen · 18 lines · 46 tokens per session scan A 5f9f0416730d
principle-guard-the-context-window is a skill published in the GitHub repository ericlitman/open-pstack (206 stars, last pushed yesterday), licensed MIT. It adds 46 tokens to every session and 242 once invoked, about $0.0002 per session on Opus 5. A static security scan graded it A with 0 findings. It is 92% identical to principle-guard-the-context-window, differing in 6 lines, and is treated as a copy.
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