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 stdin/buy-vs-build --skill buy-vs-build-decisiongit clone --depth 1 https://github.com/stdin/buy-vs-buildWrote 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/stdin/buy-vs-build/buy-vs-build-decision)<a href="https://agentmods.dev/skills/stdin/buy-vs-build/buy-vs-build-decision"><img src="https://agentmods.dev/badge/skills/stdin/buy-vs-build/buy-vs-build-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/stdin/buy-vs-build/buy-vs-build-decision"><img src="https://agentmods.dev/badge/skills/stdin/buy-vs-build/buy-vs-build-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 | $0.00042 | $0.00348 |
| Opus 5 | $0.00021 | $0.00174 |
| Sonnet 5 | $0.00008 | $0.00070 |
| Haiku 4.5 | $0.00004 | $0.00035 |
Grade A, and why
buy-vs-build-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 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.
What it actually says
Buy vs Build Decision
Make the smallest useful decision memo. The goal is clarity, not ceremony.
Workflow
- State the requirement and constraints.
- Classify it: core (differentiation) or context, and commodity (stable) or novel. Reuse context and commodity work; reserve in-house for core, novel work.
- Walk the ladder: do nothing, built-in, native platform, installed dependency, open source, commercial, in-house.
- When several options fit the rung, pick the one that matches the requirement's real shape (directionality, volume, latency, consistency, failure mode), not the most powerful, popular, or familiar one.
- Compare fit, total cost of ownership, security, licensing, maintenance, integration, maturity, reversibility, and exit risk.
- Choose the lowest-ownership option that satisfies the constraints. For hard-to-reverse (one-way-door) choices, demand more scrutiny and an exit plan.
- Name the trigger that would justify revisiting the decision.
Output
Use this format:
Decision: use <option/rung>.
Why: <one or two sentences on the winning tradeoff>.
Rejected: <main alternative> because <constraint>.
Revisit if: <specific trigger>.
If building in-house, name the reuse option that failed and the constraint it failed. If adding a dependency or service, name the built-in or installed option that was insufficient.
What ships with it
1 file 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.
- 11d ago First seen · 32 lines · 42 tokens per session scan A 5e5bb022c8cb
buy-vs-build-decision is a skill published in the GitHub repository stdin/buy-vs-build (3 stars, last pushed 2mo ago), licensed MIT. It adds 42 tokens to every session and 348 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 2026-08-31.
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