Runs on-demand, sandbox-isolated mutation testing against a single source file to identify gaps in unit test coverage. Chaos-MCP generates mutants (logical faults like changing > to >=) and checks whether the local test suite catches them. Surviving mutants indicate test coverage holes. Supports TypeScript/JavaScript (StrykerJS), Python (cosmic-ray), Rust (cargo-mutants), and PHP (Infection). PATHS: filePath is resolved against the SERVER's working directory (or given absolute). The target in the result is relative to the audited file's own WORKSPACE, which differs whenever the file sits in a monorepo package or another root — packages/api/src/math.ts comes back as src/math.ts. When the two differ the result carries workspace (an absolute path) and join(workspace, target) is a filePath you can pass straight back; when it is absent, target already is one. A file from triage_test_coverage is always a valid filePath as-is.

Batch triage: audit a set of files and/or directories and return a weakest-first ranked leaderboard of mutation scores, so you can see where the test suite is most fragile in one call. Directories are recursively expanded to supported source files (.ts/.js/.py/.rs/.php), skipping test files. Files are audited in parallel (see fileConcurrency, default min(4, cpus-1)), under a shared wall-clock budget (see totalTimeoutMs). Drill into a weak file with audit_code_resilience for per-mutant survivor detail: each row's file is relative to the server's working directory, so it can be passed straight back as that tool's filePath (its own target is spelled differently — see that tool's description).

Cheap pre-flight estimate of how big/long auditing a file will be, WITHOUT running the full mutation test cycle. Returns an approximate mutant count (for Rust, an exact count of the mutants cargo-mutants --list GENERATES — the audit scores fewer, excluding unviable ones as incompetent; a source heuristic for TS/JS/Python/PHP, labeled fidelity:"approx"). Set withTiming:true to also run the test suite once and estimate wall-clock time. Use this before audit_code_resilience to decide whether to audit now, scope down, or skip.