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 shinpr/nautilus --skill product-principlesgit clone --depth 1 https://github.com/shinpr/nautilusWrote 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/shinpr/nautilus/product-principles)<a href="https://agentmods.dev/skills/shinpr/nautilus/product-principles"><img src="https://agentmods.dev/badge/skills/shinpr/nautilus/product-principles/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/shinpr/nautilus/product-principles"><img src="https://agentmods.dev/badge/skills/shinpr/nautilus/product-principles.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 | $0.00049 | $0.01366 |
| Opus 5.5 | $0.00020 | $0.00546 |
| Sonnet 5.5 | $0.00010 | $0.00273 |
| Haiku 4.5 | $0.00005 | $0.00137 |
Grade A, and why
product-principles 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 2mo 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 — 112 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Product Management Principles
Core Philosophy
- Hypothesis Until Proven: Every assumption is a hypothesis until validated with evidence. Treat unvalidated ideas as hypotheses, not facts
- Value Traceability: Preserve the links needed to connect a decision or implementation back to its supporting outcome and evidence
- Proportionate Validation: Use cost x risk x reversibility to determine sufficient confidence
- Proportionate Artifacts: Keep durable decisions in repo artifacts when a downstream consumer will reuse them; no-change and reuse are valid outcomes
Opportunity Solution Tree (OST) Hierarchy
Use this hierarchy to distinguish outcomes, opportunities, solutions, assumptions, and experiments when those distinctions affect the current decision:
Outcome
├── Product Outcome (team-controllable product goals)
│ NSM connects Product Outcome ↔ Business Outcome
└── Business Outcome (business results Product Outcome contributes to)
Product Outcome
└── Opportunity (user problems, needs, desires)
└── Solution (approaches to address the opportunity = feature candidates)
└── Assumption (premises underlying the solution = hypotheses)
└── Experiment (methods to validate the hypothesis)
Level Definitions
| Level | Granularity | Artifact | Description |
|---|---|---|---|
| Business Outcome | Largest | docs/product/vision.md |
Business results the product contributes to |
| Product Outcome | Large | docs/product/vision.md |
Team-controllable product goals |
| Opportunity | Large | docs/discovery/opportunities/ |
User problems, needs, desires |
| Solution | Medium | PRD (docs/prd/) |
Feature candidates addressing an Opportunity |
| Assumption | Small | docs/discovery/hypotheses/ |
Premises underlying a Solution |
| User Story | Smallest | Within PRD | Minimum unit of value with sufficient evidence for its material risks |
4 Risks (Authoritative Definition)
What ships with it
2 files 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.
- 2mo ago First seen · 112 lines · 49 tokens per session scan A 8a3d7bdc0303
product-principles is a skill published in the GitHub repository shinpr/nautilus (7 stars, last pushed 8d ago), licensed MIT. It adds 49 tokens to every session and 1,366 once invoked, about $0.0002 per session on Opus 5.5. 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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