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 jenningsallen-art/second-brain-os --skill sanity-checkgit clone --depth 1 https://github.com/jenningsallen-art/second-brain-osWrote 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/jenningsallen-art/second-brain-os/sanity-check)<a href="https://agentmods.dev/skills/jenningsallen-art/second-brain-os/sanity-check"><img src="https://agentmods.dev/badge/skills/jenningsallen-art/second-brain-os/sanity-check/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/jenningsallen-art/second-brain-os/sanity-check"><img src="https://agentmods.dev/badge/skills/jenningsallen-art/second-brain-os/sanity-check.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 | $0.00169 | $0.01269 |
| Opus 5 | $0.00084 | $0.00634 |
| Sonnet 5 | $0.00034 | $0.00254 |
| Haiku 4.5 | $0.00017 | $0.00127 |
Grade A, and why
sanity-check 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 11d 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 — 109 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Sanity Check
The anti-echo-chamber skill. While thinking-partner provides frameworks, this skill does something different: it checks claims against evidence. The vault is a living record of decisions, meeting notes, and context — use it to hold the user accountable to their own prior thinking and to external reality.
When to Activate
Explicit triggers:
- "Sanity check this"
- "Am I wrong about X?"
- "Audit my assumptions"
- "What does the vault say about this?"
- "Stress test this against what we know"
Proactive triggers (use with a light touch):
- The user makes a factual claim about a project, person, or decision that can be verified in the vault
- The user's current plan contradicts something captured in a previous meeting note or decision log
- An assumption in play hasn't been re-examined in 2+ weeks (check file dates in the vault's project notes and people directory)
- The user and Claude have been in agreement for 4+ exchanges on a strategic topic without surfacing a counter-argument
- The user uses "obviously" or "everyone knows" — these phrases often mark unexamined assumptions
The Sanity Check Process
1. Identify the Claims
Extract the specific claims, assumptions, or beliefs being tested. Be precise:
- NOT: "The user thinks the strategy is good"
- YES: "The user assumes (a) the data chain will be ready by Q3, (b) the executive sponsor supports the hire, (c) the team has capacity to absorb a new tool"
2. Evidence Audit (Vault-First)
For each claim, search the vault systematically:
Check project notes in 1 - Projects/ — Is there project context that confirms or contradicts?
Check TASKS.md — Are there stale items that suggest a claim about progress is optimistic?
Check recent meeting notes in 1 - Projects/ and 2 - Areas/ — Did someone say something
in a meeting that cuts against the current assumption?
Check people profiles in 3 - Resources/ — Is the user assuming someone's position without recent validation?
Check Daily Notes/ — Has this topic come up before? What was the conclusion then?
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.
- 11d ago First seen · 109 lines · 169 tokens per session scan A b3e157620f63
sanity-check is a skill published in the GitHub repository jenningsallen-art/second-brain-os (2 stars, last pushed 1mo ago), licensed MIT. It adds 169 tokens to every session and 1,269 once invoked, about $0.0008 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 2026-08-31.
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