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 s977043/river-review --skill typescript-nullcheckgit clone --depth 1 https://github.com/s977043/river-reviewWrote 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/s977043/river-review/typescript-nullcheck)<a href="https://agentmods.dev/skills/s977043/river-review/typescript-nullcheck"><img src="https://agentmods.dev/badge/skills/s977043/river-review/typescript-nullcheck/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/s977043/river-review/typescript-nullcheck"><img src="https://agentmods.dev/badge/skills/s977043/river-review/typescript-nullcheck.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 | $0.00023 | $0.00958 |
| Opus 5 | $0.00012 | $0.00479 |
| Sonnet 5 | $0.00005 | $0.00192 |
| Haiku 4.5 | $0.00002 | $0.00096 |
Grade A, and why
TypeScript Null Safety Guardrails 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 5d 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
Pattern declaration
Primary pattern: Reviewer Secondary patterns: Inversion Why: TypeScriptコードの差分からnull/undefinedの安全性をレビューし、実行時エラーシナリオを逆照射する。
Rule / ルール
- 非同期・外部入力・オプショナル値には null/undefined ガードを設ける。
- 非 null アサーション（
!）や型アサーション（as Foo）に頼らず安全な分岐/early return を使う。 - ユニオン型は網羅的にハンドリングし、
never到達をチェックする。
Heuristics / 判定の手がかり
foo!やas Typeで未定義かもしれない値を強制している。- API レスポンス/環境変数/クエリパラメータをノーチェックで使用。
switch/ifでユニオン型の全ケースをカバーしていない（defaultで握りつぶし）。- Promise 戻りを
awaitせずに使い、undefinedアクセスの可能性がある。
Good / Bad Examples
- Good:
if (!value) return err('missing value');のように early return でガード。 - Bad:
value!.lengthのような非 null アサーション。 - Good:
switch (state.kind)で各 kind を列挙し、default: assertNever(state)を置く。
Actions / 改善案
- 外部入力やオプショナル値に対して null/undefined チェックを追加し、早期 return/throw で制御を明確化する。
- 非 null アサーションを排除し、undefined を許容する型定義やパーサーを導入する。
- ユニオン型を網羅する switch/if を書き、
assertNeverなどで漏れを検知する。
Non-goals / 扱わないこと
- 全コードベースの型定義や API 契約の再設計。
strictモードの導入可否判断。- ライブラリ側の型定義バグの修正。
Pre-execution Gate / 実行前ゲート
このスキルは以下の条件がすべて満たされない限りNO_REVIEWを返す。
- 差分にTypeScriptファイル（
*.tsまたは*.tsx）が含まれている - inputContextにdiffが含まれている
ゲート不成立時の出力: NO_REVIEW: typescript-nullcheck — TypeScriptファイルの差分がない
False-positive guards / 抑制条件
- null/undefined が型で排除され、追加ガードが不要な箇所。
asserts/バリデータで入力が保証されていると明示されている。
評価指標（Evaluation）
- 合格基準: 指摘が差分に紐づき、根拠と次アクションが説明されている。
- 不合格基準: 差分と無関係な指摘、根拠のない断定、抑制条件の無視。
人間に返す条件（Human Handoff）
- 仕様や意図が不明確で解釈が分かれる場合は質問として返す。
- 影響範囲が広い設計判断やトレードオフは人間レビューへ返す。
What ships with it
6 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.
- 5d ago First seen · 81 lines · 23 tokens per session scan A ccb1a535edbf
TypeScript Null Safety Guardrails is a skill published in the GitHub repository s977043/river-review (3 stars, last pushed today), licensed MIT. It adds 23 tokens to every session and 958 once invoked, about $0.0001 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 2026-09-03.
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