# Show HN: Whetstone – 20 Claude Code skills, each distilled from one real failure > Source: > Published: 2026-08-09 20:07:58+00:00 # Every skill here is a *scar*. Agent skills honed on real work. Each one is a short, self-contained rule set distilled from **one concrete failure** — written so an AI coding agent (or a human) can apply the lesson without the original context. ## Not general advice. A scar. ### It happened. Every skill names the sanitized case it was distilled from — a check that passed against a stand-in, a merge that dropped a field, a green test that could never fail. No hypotheticals. ### It generalizes. No project or company detail survives. The lesson is stripped to its mechanism so it transfers to your codebase, your stack, your next incident. ### It has an edge. Each ends in a pre-flight checklist that fails loudly when a box is unchecked — a gate on "done," not a suggestion you can wave through. If it reads like a blog post, it doesn't belong. If it reads like a checklist a tired engineer would thank you for at3am, it does. ## Twenty edges, grouped by grind. Each links to its `SKILL.md` — the full rule set, the sanitized case, and the pre-flight check. ### Verify & prove 06 skills[verify-through-the-real-path ↗ ](https://github.com/iamakbarsha1/whetstone/tree/main/skills/verify-through-the-real-path) #### Verify Through the Real Path Before claiming something works, is done, safe, or fast — verify through the actual trigger, real data, and representative conditions, not a stand-in. [prove-the-test-can-fail ↗ ](https://github.com/iamakbarsha1/whetstone/tree/main/skills/prove-the-test-can-fail) #### Prove the Test Can Fail After writing a test, or before trusting a green one — make it fail on purpose once, and confirm new branches are reachable by the mocks. [measure-the-delta-not-the-absolute ↗ ](https://github.com/iamakbarsha1/whetstone/tree/main/skills/measure-the-delta-not-the-absolute) #### Measure the Delta, Not the Absolute Judging whether your change is clean on a red or noisy baseline — prove it by stash-and-compare, not by which files appear in the failure list. [test-fixture-realism ↗ ](https://github.com/iamakbarsha1/whetstone/tree/main/skills/test-fixture-realism) #### Test-Fixture Realism Writing tests against a shared store or fabricated fixtures — make fixtures mirror data reality and assertions unable to pass trivially. [know-your-aggregate-command-scope ↗ ](https://github.com/iamakbarsha1/whetstone/tree/main/skills/know-your-aggregate-command-scope) #### Know Your Aggregate Command's Scope Before citing a test / lint / type-check / build script as proof — confirm what it actually runs, how it forwards args, and whether it caches. [running-long-background-jobs ↗ ](https://github.com/iamakbarsha1/whetstone/tree/main/skills/running-long-background-jobs) #### Running Long Background Jobs Launching or verifying a long-running / detached job, or reconciling a batch against a corpus other processes also write to. ### Plan & design 06 skills[plan-cross-encoding-review ↗ ](https://github.com/iamakbarsha1/whetstone/tree/main/skills/plan-cross-encoding-review) #### Plan Cross-Encoding Review Reviewing a plan or spec — catch the bug where one intent is encoded twice and the copies quietly disagree. [confirm-the-premise-first ↗ ](https://github.com/iamakbarsha1/whetstone/tree/main/skills/confirm-the-premise-first) #### Confirm the Premise First Designing when a choice depends on a technical property — state the ground truth (local vs remote, reversible vs not) before asking downstream questions. [audit-before-you-build ↗ ](https://github.com/iamakbarsha1/whetstone/tree/main/skills/audit-before-you-build) #### Audit Before You Build Starting from a ticket, checklist, or spec — grep for what already exists first; trackers record conversations, not deliverables. [inject-ambient-inputs ↗ ](https://github.com/iamakbarsha1/whetstone/tree/main/skills/inject-ambient-inputs) #### Inject Ambient Inputs Writing logic that reads the clock, randomness, env, or handles — pass them in as parameters so the pure core tests with no mocking machinery. [consistency-is-local-first ↗ ](https://github.com/iamakbarsha1/whetstone/tree/main/skills/consistency-is-local-first) #### Consistency Is Local First Adding code to an existing module — match the nearest sibling's pattern; a repo-wide convention is the default only when the module has none. [validate-the-users-proposed-mechanism ↗ ](https://github.com/iamakbarsha1/whetstone/tree/main/skills/validate-the-users-proposed-mechanism) #### Validate the User's Proposed Mechanism A user names a platform, tool, or library — treat it as a proposed mechanism; grep the artifact for disqualifiers before agreeing. ### Change safely 04 skills[grep-the-blast-radius ↗ ](https://github.com/iamakbarsha1/whetstone/tree/main/skills/grep-the-blast-radius) #### Grep the Blast Radius Changing a shared contract (flag, column, type, endpoint) — the retired name is your consumer index; grep the whole workspace and run cross-boundary suites. [diff-each-side-against-merge-base ↗ ](https://github.com/iamakbarsha1/whetstone/tree/main/skills/diff-each-side-against-merge-base) #### Diff Each Side Against the Merge Base Resolving a merge or rebase conflict — markers show where git gave up, not the full delta; auto-merge silently drops fields. [verify-absence-claims ↗ ](https://github.com/iamakbarsha1/whetstone/tree/main/skills/verify-absence-claims) #### Verify Absence Claims Acting on a "none exists / not found" claim, especially from delegated research — re-grep it; absence is only as good as the search pattern. [negative-invariant-testing ↗ ](https://github.com/iamakbarsha1/whetstone/tree/main/skills/negative-invariant-testing) #### Negative-Invariant Testing Protecting a "never does X" constraint — a behavioural test can't see an unused capability; assert structurally on the mechanism's existence. ### Diagnose & review 03 skills[read-the-real-failing-call ↗ ](https://github.com/iamakbarsha1/whetstone/tree/main/skills/read-the-real-failing-call) #### Read the Real Failing Call Hardening against a failure mode — instrument the real failing call before and after, because a plausible hypothesis is not a diagnosis. [manufacture-review-independence ↗ ](https://github.com/iamakbarsha1/whetstone/tree/main/skills/manufacture-review-independence) #### Manufacture Review Independence Reviewing your own work (author == reviewer) — replace lost independence with scoped parallel passes and adversarial re-reads of the source. [findings-list-is-not-a-todo-list ↗ ](https://github.com/iamakbarsha1/whetstone/tree/main/skills/findings-list-is-not-a-todo-list) #### A Findings List Is Not a To-Do List Acting on a review or audit list — re-read each item's disposition and bucket them; some are marked no-fix, some need a human decision. ## Same shape, every time. One folder, one `SKILL.md` . Plain Markdown, so any agent that can load a system prompt can use it — the plugin auto-discovery is the only Claude Code-specific part. - frontmatter #### name + description The description carries the trigger phrases, so a skill-aware agent surfaces the right skill when the situation matches. - the rule #### The core rule One paragraph. The whole lesson, stated once, before any elaboration. - the cases #### Checks Each rule paired with the sanitized real case it came from — the scar that earned it. - the gate #### Pre-flight check The checklist that gates "done" and fails loudly when a box is unchecked. ## Install Two ways in. The plugin gives you auto-discovery; the manual copy is just folders. ### Claude Code plugin Add the marketplace, then install the plugin — all 20 skills come with it. Run both inside Claude Code. ### Manual copy Each skill is a self-contained folder in the Claude Code skill layout. Copy one, or all of them.