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/backnotprop/pstack/principle-guard-the-context-windownpx skills add backnotprop/pstack --skill principle-guard-the-context-windowgit clone --depth 1 https://github.com/backnotprop/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/backnotprop/pstack/principle-guard-the-context-window)<a href="https://agentmods.dev/skills/backnotprop/pstack/principle-guard-the-context-window"><img src="https://agentmods.dev/badge/skills/backnotprop/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 | $0.00243 |
| Opus 5 | $0.00023 | $0.00121 |
| Sonnet 5 | $0.00009 | $0.00049 |
| 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 4d 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.
Copies of this mod
4 near-identical copies found in the catalogue:
- principle-guard-the-context-window — 95% identical, 2 lines differ
- principle-guard-the-context-window — 95% identical, 2 lines differ
- principle-guard-the-context-window — 94% identical, 1 lines differ
- principle-guard-the-context-window — 92% identical, 4 lines differ
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.
- 4d ago First seen · 18 lines · 46 tokens per session scan A 291d0125125e
principle-guard-the-context-window is a skill published in the GitHub repository backnotprop/pstack (193 stars, last pushed 15d ago), licensed MIT. It adds 46 tokens to every session and 243 once invoked, about $0.0002 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.
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