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 ericlitman/open-pstack --skill principle-type-system-disciplinegit clone --depth 1 https://github.com/ericlitman/open-pstackWrote 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/ericlitman/open-pstack/principle-type-system-discipline)<a href="https://agentmods.dev/skills/ericlitman/open-pstack/principle-type-system-discipline"><img src="https://agentmods.dev/badge/skills/ericlitman/open-pstack/principle-type-system-discipline/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/ericlitman/open-pstack/principle-type-system-discipline"><img src="https://agentmods.dev/badge/skills/ericlitman/open-pstack/principle-type-system-discipline.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 | $0.00053 | $0.00312 |
| Opus 5.5 | $0.00021 | $0.00125 |
| Sonnet 5.5 | $0.00011 | $0.00062 |
| Haiku 4.5 | $0.00005 | $0.00031 |
Grade A, and why
principle-type-system-discipline 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 9d 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.
This is a copy
100% identical to principle-type-system-discipline — 0 lines differ, which has more behind it and is treated as the original. This page carries a canonical link to it rather than competing with it.
What it actually says
Type System Discipline
Make the compiler reject impossible states, mismatched primitives, and unhandled variants. Prefer defining errors and special cases out of existence over proliferating handlers. For TypeScript syntax, see the typescript-best-practices skill.
- Brand semantic primitives.
UserIdandOrderIdare strings underneath but should not be interchangeable. Give each its own type, such as a branded intersection in TypeScript or a newtype elsewhere. Validate once at creation, trust the type downstream. If two arguments share a primitive type but mean different things, brand them. - External data is untyped until parsed. RPC payloads, JSON, IPC messages, CLI args, config files, environment variables, database rows. Have a parse function at every boundary that turns unstructured input into the typed model. The boundary-discipline principle skill says where to put validation.
- Derive types from authoritative schemas. When a protocol buffer, OpenAPI spec, GraphQL schema, database migration, design-token file, or another file owns a shape, derive from it instead of hand-rolling a parallel type. See the encode-lessons-in-structure principle skill.
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.
- 9d ago Changed · -5 lines · -7 tokens per session e4bb75104ff5
- 14d ago Changed · -13 lines 388d8966513f
- 1mo ago Changed adaa7a27c879
- 1mo ago First seen · 32 lines · 60 tokens per session scan A 5b4df1580055
principle-type-system-discipline is a skill published in the GitHub repository ericlitman/open-pstack (526 stars, last pushed 2d ago), licensed MIT. It adds 53 tokens to every session and 312 once invoked, about $0.0002 per session on Opus 5.5. A static security scan graded it A with 0 findings. It is 100% identical to principle-type-system-discipline, differing in 0 lines, and is treated as a copy.
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