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 SkillMedev/skills --skill big-purchase-decisiongit clone --depth 1 https://github.com/SkillMedev/skillsWrote 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/skillmedev/skills/big-purchase-decision)<a href="https://agentmods.dev/skills/skillmedev/skills/big-purchase-decision"><img src="https://agentmods.dev/badge/skills/skillmedev/skills/big-purchase-decision/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/skillmedev/skills/big-purchase-decision"><img src="https://agentmods.dev/badge/skills/skillmedev/skills/big-purchase-decision.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 | $0.00122 | $0.01805 |
| Opus 5 | $0.00061 | $0.00903 |
| Sonnet 5 | $0.00024 | $0.00361 |
| Haiku 4.5 | $0.00012 | $0.00180 |
Grade A, and why
Big Purchase Decision 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 10d 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 — 108 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Big Purchase Decision
Big purchases feel like one-time decisions but are almost always multi-year financial commitments. The costly mistake this skill prevents is deciding on sticker price and monthly payment - the two numbers sellers control - instead of total cost, opportunity cost, and affordability. Analyze before signing, because afterward the analysis is just regret.
Operating procedure
Step 1: Confirm the purchase clears the threshold
Apply the full framework to any single purchase above 1% of annual take-home income (for most households, $500-$1,500). Two lighter rules cover everything below it:
- Below the 1% threshold but still discretionary and unplanned: apply the 24-hour rule - sleep on it once. Most impulse purchases do not survive one night.
- A useful ceiling for guilt-free discretionary buys: anything under 1% of net worth rarely warrants analysis for households with positive net worth; above that, it does.
Non-urgent purchases above the 1%-of-income threshold get the 30-day rule: wait 30 days before buying. Most impulse-driven desires fade within that window; a desire still strong at day 30 that also passes the financial tests below is a considered want, not an impulse.
Step 2: Gather inputs
- Purchase price and how it would be paid (cash, financing terms, APR).
- Annual take-home income and current monthly surplus (from budget-builder if one exists).
- Ownership costs: insurance change, maintenance, fuel/consumables, registration or subscription fees, expected useful life. Label estimates as estimates.
- Emergency fund status and any debt above 7-8% APR - both are gate conditions in Step 5.
Step 3: Compute total cost of ownership
TCO = price + financing interest + (annual insurance delta + maintenance + consumables + fees) × years of useful life. Divide by useful life for true annual cost. A $25,000 vehicle typically lands at $8,000-$12,000 per year once interest, insurance, fuel, maintenance, and depreciation are loaded - three to four times what the sticker suggests.
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.
- 10d ago First seen · 108 lines · 122 tokens per session scan A db195ab6d500
Big Purchase Decision is a skill published in the GitHub repository SkillMedev/skills (11 stars, last pushed 2mo ago), licensed MIT. It adds 122 tokens to every session and 1,805 once invoked, about $0.0006 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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