Performance

mdwright is parallel by default (rayon over the file walk) and free of per-file interpreter startup. On a multi-thousand-file corpus the practical speedup over mdformat --check is the dominant cost difference; on small inputs both tools are sub-second and the comparison is dominated by process startup.

Measurement

Reproducer:

hyperfine --warmup 2 --runs 7 -N -i \
  './target/release/mdwright fmt-check <corpus>' \
  'mdformat --check <corpus>'

• Corpus: 79 Markdown files, ~34.5k lines of math-heavy technical prose (a checkout of gentle-sga).
• Host: Apple M4 Pro, macOS 26.4.1.
• Versions: mdwright from this workspace, release profile; mdformat 0.7 (default plugins).
• Result: 55× ± 6×. The lede claim of "≥ 50× faster" is the floor of this measurement.

What changes the multiplier

• File count. mdwright's startup is fixed; mdformat re-pays interpreter cost per file when invoked per-file. On directory invocations both tools amortise startup over the walk, but mdformat still single-threads the loop.
• Core count. mdwright scales with rayon's thread pool. On a single-core machine the multiplier drops; on a 16-core CI runner with a large corpus it climbs.
• File size. Per-byte parse cost is closer than the wall-time ratio suggests; on a single very large file, the ratio approaches the per-byte ratio rather than the per-file ratio.

Reproducing locally

The bench harness used in development is Criterion, not hyperfine. See crates/mdwright/benches/README.md for cargo bench recipes and corpus configuration. The hyperfine command above is the end-to-end smoke test; the Criterion benches isolate parse, lint, and format costs separately.