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 uqeu/estelle-cli --skill mutation-testgit clone --depth 1 https://github.com/uqeu/estelle-cliWrote 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/uqeu/estelle-cli/mutation-test)<a href="https://agentmods.dev/skills/uqeu/estelle-cli/mutation-test"><img src="https://agentmods.dev/badge/skills/uqeu/estelle-cli/mutation-test/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/uqeu/estelle-cli/mutation-test"><img src="https://agentmods.dev/badge/skills/uqeu/estelle-cli/mutation-test.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 | $0.00000 | $0.00275 |
| Opus 5.5 | $0.00000 | $0.00110 |
| Sonnet 5.5 | $0.00000 | $0.00055 |
| Haiku 4.5 | $0.00000 | $0.00028 |
Grade A, and why
mutation-test 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 1mo 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
mutation-test
A state-of-the-art engineering playbook, drawn from Google 'State of Mutation Testing at Google' / PIT, that an agent grounding in a real repo can execute. Every referenced symbol is checked by Estelle's grounding gate like any other code.
When to run
Before trusting a green suite / high coverage as real safety — especially on critical logic where a passing-but-vacuous test would hide a bug.
Procedure
- Run a mutation tool (mutmut/cosmic-ray for Python) on the target module: it flips operators, boundaries, and returns.
- A SURVIVING mutant = a fault the suite didn't catch = a missing assertion. Rank survivors by how central the mutated line is.
- Write the assertion that kills each high-value survivor; ignore equivalent mutants.
- Report the mutation score alongside coverage — coverage says 'executed', mutation says 'checked'.
Grounding note
Apply this to the caller's ACTUAL code (the code graph + real symbols), not a generic template — the value is a concrete, verifiable change on their repo, not advice.
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.
- 1mo ago First seen · 21 lines · 0 tokens per session scan A 73a83582d1f8
mutation-test is a skill published in the GitHub repository uqeu/estelle-cli (0 stars, last pushed 14d ago), licensed Apache-2.0. It costs nothing until one of its globs matches a file; then it loads 275 tokens. 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 2026-09-12.
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