kumo

An async web crawling framework for Rust - Scrapy for Rust.

kumo means spider/cloud in Japanese. It gives you a trait-based, async-first API for writing spiders that scrape, follow links, and store data.

Why Kumo?

Benchmark results - 1,000 books, concurrency 16, median of 3 runs:

On raw parsing throughput (local server, no network): 3.0x faster than Colly, 69x faster than Scrapy. See the benchmark folder for full methodology and reproduction steps.

Features

• Async-first - Tokio-based with bounded concurrency via JoinSet
• CSS selectors - res.css(".selector") backed by scraper
• XPath selectors - res.xpath("//h1/text()") for XML/HTML documents (feature: xpath)
• Regex selectors - res.re(r"\d+"), el.re_first(r"..."), works on Response, Element, and ElementList
• JSONPath selectors - res.jsonpath("$.store.books[*].title") for JSON responses (feature: jsonpath)
• #[derive(Extract)] - generate CSS extraction boilerplate from field annotations (feature: derive)
• Rate limiting - token-bucket RateLimiter via governor
• Auto-throttle - adaptive delay based on EWMA latency and 429/503 back-off
• Retry with backoff - exponential backoff, status filtering, jitter, and Retry-After support
• Item stream - CrawlEngine::stream() returns an async Stream for real-time item consumption
• robots.txt - per-domain fetch + cache, enabled by default, with Crawl-delay support
• Bloom filter dedup - O(1) URL deduplication, 1M URLs at 0.1% false-positive rate
• Request scheduling - CrawlRequest supports priority, headers, method/body, metadata, and dont_filter
• HTTP cache - disk-backed response cache via .http_cache(dir), optional TTL
• Link extractor - LinkExtractor with allow/deny regex, allow_domains, canonicalize, restrict_css
• Pluggable storage - JsonlStore, JsonStore, CsvStore, StdoutStore, PostgreSQL, SQLite, MySQL
• Middleware chain - proxy rotation, custom headers, status retry, rate limiting, auto-throttle
• Domain + depth filtering - allowed_domains() and max_depth() on the Spider trait
• Multi-spider engine - run multiple spiders concurrently via .add_spider() / .run_all()
• LLM extraction - extract structured data without selectors using Claude, OpenAI, Gemini, or Ollama
• Browser fetcher - headless Chromium via chromiumoxide for JS-rendered pages (feature: browser)
• Distributed frontier - Redis-backed URL frontier for multi-process crawls (feature: redis-frontier)
• Persistent frontier - file-backed URL frontier that survives restarts and exposes recovered state (feature: persistence)
• Sitemap spider - SitemapSpider reads sitemap.xml and sitemap index files
• Metrics - periodic stats snapshots via tracing::info! using .metrics_interval()
• OpenTelemetry - OTLP/gRPC export of all spans to Jaeger, Grafana Tempo, Datadog, etc. (feature: otel)

Installation

[dependencies]
kumo = "0.2"
async-trait = "0.1"
serde = { version = "1", features = ["derive"] }
tokio = { version = "1", features = ["full"] }

For #[derive(Extract)]:

kumo = { version = "0.2", features = ["derive"] }

Quick Start

use kumo::prelude::*;
use serde::Serialize;

#[derive(Debug, Serialize)]
struct Quote {
    text: String,
    author: String,
}

struct QuotesSpider;

#[async_trait::async_trait]
impl Spider for QuotesSpider {
    type Item = Quote;

    fn name(&self) -> &str { "quotes" }

    fn start_urls(&self) -> Vec<String> {
        vec!["https://quotes.toscrape.com".into()]
    }

    async fn parse(&self, res: &Response) -> Result<Output<Self::Item>, KumoError> {
        let quotes: Vec<Quote> = res.css(".quote").iter().map(|el| Quote {
            text:   el.css(".text").first().map(|e| e.text()).unwrap_or_default(),
            author: el.css(".author").first().map(|e| e.text()).unwrap_or_default(),
        }).collect();

        let next = res.css("li.next a").first()
            .and_then(|el| el.attr("href"))
            .map(|href| res.urljoin(&href));

        let mut output = Output::new().items(quotes);
        if let Some(url) = next { output = output.follow(url); }
        Ok(output)
    }
}

#[tokio::main]
async fn main() -> Result<(), KumoError> {
    CrawlEngine::builder()
        .concurrency(5)
        .middleware(DefaultHeaders::new().user_agent("kumo/0.2"))
        .store(JsonlStore::new("quotes.jsonl")?)
        .run(QuotesSpider)
        .await?;
    Ok(())
}

For more examples - production crawl controls, rate limiting, database stores, LLM extraction, browser mode, and all selector types - see the examples/ folder.

Documentation

Full documentation at kumo.wihlarkop.com

• Getting Started
• Spiders
• Extractors
• derive(Extract)
• Middleware
• Stores
• Advanced topics - item stream, OpenTelemetry, stealth, browser, and more
• Examples
• Feature Flags

Contributing

# Install lefthook (one-time setup)
# macOS
brew install lefthook

# Windows
scoop install lefthook
# or: winget install lefthook

# Linux
curl -1sLf 'https://dl.lefthook.dev/setup.sh' | sh

# Activate the hooks
lefthook install

After lefthook install, every git commit will automatically run cargo fmt (auto-fix) and cargo clippy before the commit goes through.

License

MIT