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 slopstopper/plumb-line --skill plumb-line-methodgit clone --depth 1 https://github.com/slopstopper/plumb-lineWrote 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/slopstopper/plumb-line/plumb-line-method)<a href="https://agentmods.dev/skills/slopstopper/plumb-line/plumb-line-method"><img src="https://agentmods.dev/badge/skills/slopstopper/plumb-line/plumb-line-method/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/slopstopper/plumb-line/plumb-line-method"><img src="https://agentmods.dev/badge/skills/slopstopper/plumb-line/plumb-line-method.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 | $0.00194 | $0.04480 |
| Opus 5.5 | $0.00078 | $0.01792 |
| Sonnet 5.5 | $0.00039 | $0.00896 |
| Haiku 4.5 | $0.00019 | $0.00448 |
Grade A, and why
plumb-line-method 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 23d 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 — 276 lines — stays where its author put it; the contents beside it link to each section on GitHub.
The plumb-line method
Read reference/portable-principles.md (relative to the plugin root) and teach
from it. Do not restate the principles here — that file is the single source.
If the file cannot be read, stop immediately and report: "Cannot teach: reference/portable-principles.md is missing or unreadable. Do not continue from memory."
If you were invoked in the middle of a task, go straight to the section for that moment; the walk can wait. A failing test or red CI that has to be made to pass, where the reason may lie outside the code: Mid-task: a test that cannot pass honestly. Any other edit that would make something look more real, finished or certain than it is: Mid-task: other moments.
When invoked:
- Read the principles document.
- Give the builder the thesis and the spine (null results are valid) first.
- Walk the nine principles only as deep as asked; lead with the one most relevant to what the builder is doing.
- Always end on the one-line test as the portable gut-check.
- Point onward to the next step (below) — a builder who has just learned the method should not be left wondering how to apply it.
This skill never edits files or installs anything.
Mid-task: a test that cannot pass honestly
The moment: you have been asked to make a failing test pass, or CI green, and the reason it fails is outside the code you can change. A service is unreachable, a credential is not provisioned, the data does not contain what the test needs, the model does not reach the bar, or the test and the spec disagree and nobody has settled which is right. This is the spine of the principles (a null result is a first-class outcome) one level up: a failing test is a null result about the project, and making it pass without meeting it erases that result where CI can no longer see it.
This skill still edits nothing. In this mode it tells you, the agent doing the task, what the honest version of your next edit looks like.
What this does not forbid
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.
- 23d ago Changed · +11 lines 6da306645c98
- 26d ago Changed · +1 lines 7b9d207e6e76
- 28d ago Changed · +168 lines · +135 tokens per session 1d1ccdd8a8cd
- 1mo ago Changed 5d631b221e55
- 1mo ago First seen · 96 lines · 59 tokens per session scan A 88e6882a68e3
plumb-line-method is a skill published in the GitHub repository slopstopper/plumb-line (4 stars, last pushed yesterday), licensed Apache-2.0. It adds 194 tokens to every session and 4,480 once invoked, about $0.0008 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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