The latest articles on DEV Community by vun (@vunholy). https://dev.to/vunholy https://media2.dev.to/dynamic/image/width=90,height=90,fit=cover,gravity=auto,format=auto/https:%2F%2Fdev-to-uploads.s3.amazonaws.com%2Fuploads%2Fuser%2Fprofile_image%2F3908215%2F9e0c8ffb-2ef1-4901-bb7f-8ba293d20f78.jpg https://dev.to/vunholy en vun Fri, 01 May 2026 22:42:37 +0000 https://dev.to/vunholy/why-i-built-cargo-feat-a-10ms-solution-to-feature-lookup-friction-50ja https://dev.to/vunholy/why-i-built-cargo-feat-a-10ms-solution-to-feature-lookup-friction-50ja <h2> The Problem </h2> <p>Every time I add a dependency to Cargo.toml, I need to know what features<br> it exposes. Current workflow:</p> <ol> <li>Open browser</li> <li>Search crates.io or docs.rs</li> <li>Scroll through documentation</li> <li>Find the feature list</li> <li>Close browser</li> </ol> <p>Repeat 20 times a day. Annoying.</p> <p>Existing tools like <code>cargo info</code> exist but are slow (80ms+).</p> <h2> The Solution </h2> <p>Built cargo-feat. Single command. Shows every feature, marks defaults, <br> lists what each feature pulls in.<br> </p> <div class="highlight js-code-highlight"> <pre class="highlight plaintext"><code>$ feat reqwest — reqwest's features are in the following list — ★ default default-tls charset http2 system-proxy — blocking — brotli — charset (default) ... </code></pre> </div> <p>Done in 9.9ms.</p> <h2> Why It's Fast </h2> <p>Three optimizations:</p> <ol> <li><p><strong>Sparse registry index</strong> — reads crates.io sparse index directly <br> (via Cloudflare CDN). Cargo uses same source. Faster than REST API.</p></li> <li><p><strong>Local cache first</strong> — checks ~/.cargo/registry/index/ before network.<br> If you've ever built with this crate, result is instant.<br> After network fetch, written to cache. Next run: always fast.</p></li> <li><p><strong>Early-stop parsing</strong> — scans index from end, stops at first stable <br> version. O(1) entries instead of O(n versions).</p></li> </ol> <p>Also uses MiMalloc + simd-json for JSON parsing.</p> <h2> Benchmarks </h2> <p>(Include table from README or simple comparison)<br> </p> <div class="highlight js-code-highlight"> <pre class="highlight console"><code><span class="go">cargo feat reqwest 9.9 ms cargo info reqwest 92.7 ms (9.4x slower) </span></code></pre> </div> <p>Works same speed for serde (180+ versions). Lookup time flat <br> regardless of version count.</p> <h2> Installation </h2> <div class="highlight js-code-highlight"> <pre class="highlight shell"><code>cargo <span class="nb">install </span>cargo-feat </code></pre> </div> <p>Then use it:<br> </p> <div class="highlight js-code-highlight"> <pre class="highlight shell"><code>feat reqwest <span class="c"># latest version</span> feat tokio 1.35.0 <span class="c"># specific version</span> feat reqwest <span class="nt">--deps</span> <span class="c"># show dependencies</span> feat reqwest <span class="nt">--internals</span> <span class="c"># show internal features</span> feat serde <span class="nt">--json</span> <span class="c"># raw JSON output</span> </code></pre> </div> <h2> Try It </h2> <div class="ltag-github-readme-tag"> <div class="readme-overview"> <h2> <img src="https://assets.dev.to/assets/github-logo-5a155e1f9a670af7944dd5e12375bc76ed542ea80224905ecaf878b9157cdefc.svg" alt="GitHub logo"> <a href="https://github.com/vunholy" rel="noopener noreferrer"> vunholy </a> / <a href="https://github.com/vunholy/cargo-feat" rel="noopener noreferrer"> cargo-feat </a> </h2> <h3> Fast CLI tool for Rust that instantly lists a crate’s features from crates.io without opening a browser. Shows default features, dependencies, and metadata with minimal overhead and optimized lookup performance. Built for speed-focused workflows. </h3> </div> <div class="ltag-github-body"> <div id="readme" class="md"> <div class="markdown-heading"> <h1 class="heading-element">cargo-feat</h1> </div> <p><a href="https://crates.io/crates/cargo-feat" rel="nofollow noopener noreferrer"><img src="https://camo.githubusercontent.com/e567ad023c37295193329bb58f3ee622fd946e38151301ec5eed705790347a0f/68747470733a2f2f696d672e736869656c64732e696f2f6372617465732f762f636172676f2d666561742e737667" alt="crates.io"></a></p> <p>A fast command-line tool for Rust developers to instantly look up the available features of any crate on <a href="https://crates.io" rel="nofollow noopener noreferrer">crates.io</a> - directly in your terminal, with no browser required.</p> <div class="markdown-heading"> <h2 class="heading-element">Why</h2> </div> <p>When adding a dependency, finding out what features it exposes usually means opening a browser, searching crates.io or docs.rs, and scrolling through documentation. <code>cargo-feat</code> removes that friction: one command gives you a color-coded list of every feature the crate exposes, which ones are enabled by default, and what each feature pulls in.</p> <div class="markdown-heading"> <h2 class="heading-element">Demo</h2> </div> <div class="snippet-clipboard-content notranslate position-relative overflow-auto"><pre class="notranslate"><code>$ feat reqwest — reqwest's features are in the following list — ★ default default-tls charset http2 system-proxy — blocking — brotli — charset (default) — cookies — default-tls (default) — deflate — gzip — http2 (default) — ... </code></pre></div> <div class="markdown-heading"> <h2 class="heading-element">Installation</h2> </div> <div class="markdown-heading"> <h3 class="heading-element">From crates.io</h3> </div> <div class="highlight highlight-source-shell notranslate position-relative overflow-auto js-code-highlight"> <pre>cargo install cargo-feat</pre> </div> <div class="markdown-heading"> <h3 class="heading-element">From source</h3> </div> <p>Requires a recent stable <a href="https://rustup.rs/" rel="nofollow noopener noreferrer">Rust toolchain</a>.</p> <div class="highlight highlight-source-shell notranslate position-relative overflow-auto js-code-highlight"> <pre>git clone https://github.com/vunholy/cargo-feat.git <span class="pl-c1">cd</span> cargo-feat cargo build --release</pre> </div> <p>The compiled binary will be…</p> </div> </div> <div class="gh-btn-container"><a class="gh-btn" href="https://github.com/vunholy/cargo-feat" rel="noopener noreferrer">View on GitHub</a></div> </div> <p>Open to feedback. Built this to scratch personal itch, <br> figured others had same problem.</p> <p>If you found it interesting, please do star it makes my day :D</p> rust cargo tooling performance