Hey r/rust 👋

I'm the author of jscpd — a copy/paste detection CLI tool for source code, supporting 223 languages/formats. It's been around for years as a TypeScript/Node.js tool. Starting with v5, I rewrote the core engine in Rust.

Here are the actual benchmark numbers (10 runs, Apple Silicon, v4.2.5 Node.js vs v5.0.4 native binary):

Target                         v4 (Node.js)   v5 (Rust)   Speedup
───────────────────────────────────────────────────────────────────
fixtures  (548 files,  1.5 MB)     1.030s      0.030s      34.3x
svelte    (9K files,  164 MB)     15.803s      0.428s      36.9x
CopilotKit (17K files, 902 MB)   82.890s      3.440s      24.1x

A few things that stand out from the data:

Startup overhead is gone. On the tiny fixtures run, v4 takes 1.03s — that's almost entirely Node.js startup. v5 is 0.03s, consistent to the millisecond across all 10 runs (std dev: 0.000s).

Multi-threading shows up clearly. On CopilotKit, v5 reports 7.3s user time vs 3.4s real time — it's genuinely using multiple cores. v4 is strictly single-threaded (user ≈ real throughout).

Blame mode is a special story. v4 shells out to git blame per file, which tanks its --blame performance badly (3.57s vs 1.03s baseline — a 3.5x regression from its own non-blame mode). v5 uses gitoxide for in-process blame, so --blame adds only ~0.10s. Same feature, night and day.

Detection improved too. v5 finds more clones on large codebases — on CopilotKit, 22,487 vs 12,272 clones — likely due to better token counting and different maxSize defaults.

The CLI is still installable via npm (npm i -g jscpd) since most users are in the JS ecosystem, but under the hood it's a native binary now. Pre-built binaries for Linux/macOS/Windows ship with each release.

The 223-language support survived the rewrite intact — everything from TypeScript and Rust to COBOL, Terraform, and Solidity.

Would love any feedback from the Rust community on the implementation — especially around the tokenizer architecture and language registry design. Code at github.com/kucherenko/jscpd, site at jscpd.dev.

Happy to answer questions about the rewrite process or the profiling methodology.

Hi everyone! 👋

I'm fairly new here, so I hope this kind of post is welcome — please let me know if there's a better place to share it!

I just wanted to give a heads-up that jscpd v4.2.0 has landed with official Svelte support, and I thought the community might find it genuinely useful.

What is jscpd?

If you haven't come across it before, jscpd is a copy/paste detector for source code. It scans your project, finds duplicated blocks across files, and reports them — a really handy tool for spotting technical debt before it piles up. It supports 150+ languages and formats, and now .svelte is officially one of them.

Why does this matter for us?

Svelte's component model makes it wonderfully easy to build UIs quickly — but in larger projects it's easy to accidentally duplicate logic across components: repeated event handlers, similar reactive declarations, copy-pasted template sections. Having a tool that understands .svelte file structure (rather than just treating them as plain text) means you can actually catch those patterns automatically.

Getting started is pretty simple:

npm install -g jscpd
jscpd --format svelte ./src

You can also add it to your CI pipeline with a threshold to fail the build if duplication gets too high:

jscpd --format svelte --threshold 5 ./src

I've been wanting this for a while in my own Svelte projects, so I was really happy to see it land. Huge thanks to the maintainers for making it happen! 🙏

Full changelog here if you're curious: https://github.com/kucherenko/jscpd/blob/master/CHANGELOG.md

Hope this is helpful to someone — happy to answer any questions if I can! 😊