🤖 Overview

Y!J is a web crawler operated by Yahoo Japan Corporation, the Japanese subsidiary of Yahoo (now part of LINE and Z Holdings). Its primary purpose is to index publicly accessible web pages for the Yahoo Japan Search engine (search.yahoo.co.jp) and to feed data into related services such as Yahoo Japan News and product listings. This bot is distinct from the global Yahoo Slurp crawler and is specifically optimized for Japanese-language content and regional web infrastructure.

🌐 Technical Behavior

Y!J typically performs HTTP requests from IP addresses belonging to Yahoo Japan’s AS (AS23877, AS9595, among others), with user-agent string variations such as "Y!J (compatible; Y!J; +https://help.yahoo.co.jp/help/jp/search/indexing/indexing-15.html)" or simply "Y!J". The crawler uses HTTP/1.1 and respects the Accept-Language header, often requesting pages with ja as preferred language. It employs a polite crawling strategy with a default delay of several seconds between requests to the same host, but can increase frequency for high‑priority domains. Y!J supports If-Modified-Since and ETag headers to avoid re‑downloading unchanged content. Official documentation (https://help.yahoo.co.jp/help/jp/search/indexing/indexing-15.html) states that the bot collects only public HTML pages and does not follow JavaScript redirects or parse dynamically loaded content.

📋 robots.txt Compliance

Y!J fully observes robots.txt directives. Yahoo Japan’s official help pages explicitly state that webmasters can block the crawler using Disallow: / for the Y!J user‑agent token. The bot also honors Crawl-Delay directives if present. There are no confirmed reports of Y!J ignoring robots.txt rules; its compliance is verified through both documentation and real‑world testing by webmasters in Japan.

🔍 Detection Indicators

The primary User‑Agent strings are Y!J (compatible; Y!J; +https://help.yahoo.co.jp/help/jp/search/indexing/indexing-15.html) and the abbreviated Y!J. Behavioral fingerprints include the use of Accept: text/html,application/xhtml+xml and a distinctive From header (rarely). The bot’s reverse DNS often resolves to *.yjc.ynl.co.jp or similar Yahoo Japan infrastructure. It does not send cookies or parse JavaScript.

📊 Data Usage

Collected content is primarily used for Yahoo Japan’s search index, powering both organic results and features like “Yahoo!知恵袋” (Yahoo Answers Japan) and news aggregation. Additionally, extracted metadata may be used for AI‑powered summarisation and snippet generation within Yahoo Japan Search. There is no public evidence that Y!J data is used for training large language models outside of Yahoo Japan’s own text analytics initiatives.

⚙️ Rate Limiting Policy

Y!J is rate‑limited because its relatively high request volume—especially during index refreshes—can impact server resources on smaller websites. Threshold‑based blocking (e.g., limiting requests per IP per minute) is recommended to ensure fair resource allocation while still allowing the legitimate crawler to index content for Yahoo Japan users.

ⓘ Data Notice: The information presented above has been compiled from publicly available internet sources. Boteraser aggregates this data solely for informational purposes and does not independently classify, evaluate, or endorse any findings about the bots listed. The accuracy and completeness of this information is the sole responsibility of the original publishers. Boteraser and its operators accept no liability for any decisions made based on this data.