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 agentmods add skills/nerds-odd-e/doughnut/mutation-testingnpx skills add nerds-odd-e/doughnut --skill mutation-testinggit clone --depth 1 https://github.com/nerds-odd-e/doughnutWhat 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 | $0.00035 | $0.01042 |
| Opus 5 | $0.00017 | $0.00521 |
| Sonnet 5 | $0.00007 | $0.00208 |
| Haiku 4.5 | $0.00003 | $0.00104 |
Grade A, and why
mutation-testing 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 2d 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 — 116 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Purpose: Validate that unit tests exercise module logic after extract/refactor, or compare broad boundary coverage vs mutation kill rate on pure/narrow modules.
Output: Mutation run results + interpretation + summary ending with
## MUTATION TEST COMPLETE.
Current scope: cli/ only. Later: reuse in frontend/, mcp-server/.
Git does not use the Nix prefix. All other repo tooling does:
CURSOR_DEV=true nix develop -c …
Policy on survived mutants: A survived mutant means no test executes that branch — or the code is dead/unreachable. Do not automatically add tests. First consider delete dead path, merge redundant logic, or prove the code is still required from product/domain behavior.
Follow always-applied .cursor/rules/unit-testing.mdc ("small test" style: stable
boundary, data over mocks, focused assertions).
Do not add shallow tests that reach into inner structure, call non-entry-point helpers, or assert on internal state just to flip Stryker green.
Do add or extend coverage by driving a stable boundary (controller,
mounted page, runInteractive, real CLI) with crafted preconditions so lower
layers run for real. Assert only what a user or integrator can observe: HTTP
response, CLI stdout, DOM, black-box inputs/outputs.
Pure helpers (inputs → result, no hidden globals) may keep direct-import black-box unit tests only when that API is the intentional stable contract.
If a good observable test is hard to compose, ask the developer whether the mutated code deserves to exist.
<success_criteria>
- Mutation run executed with Nix prefix (
cli/scope unless extending) - Survived mutants interpreted per policy (no auto shallow tests)
- Developer consulted when observable coverage is hard to compose
- Final output includes
## MUTATION TEST COMPLETE</success_criteria>
## MUTATION TEST COMPLETE
<out_of_scope>
- Do not run proactively without explicit developer or plan request.
- Do not add tests that only pin internal structure to kill mutants.
- Do not extend beyond
cli/unless followingextend_to_subproject. </out_of_scope>
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.
- 2d ago First seen · 116 lines · 35 tokens per session scan A f732188775bb
mutation-testing is a skill published in the GitHub repository nerds-odd-e/doughnut (49 stars, last pushed 2d ago), licensed MIT. It adds 35 tokens to every session and 1,042 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 2026-08-30.
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