What is polite crawling?
TL;DR
Polite crawling means respecting website resources by limiting request rates, following robots.txt rules, and monitoring server responses. Most crawlers wait 10-15 seconds between requests, but this varies based on domain size, server response time, and explicit crawl-delay directives. Without polite crawling, your crawler risks getting blocked and can cause server overload.
What is Polite Crawling?
Polite crawling is the practice of accessing websites in a respectful manner that avoids overwhelming servers or consuming excessive resources. Crawlers follow politeness rules by spacing out requests, honoring access restrictions, and adapting to server performance. The concept exists because automated crawlers can make hundreds of requests per second, something no human user would do, potentially crippling website performance.
Why Polite Crawling Matters
Website servers have finite resources. When crawlers make too many requests too quickly, they consume bandwidth, processing power, and memory that should serve actual users. Small websites hosted on limited infrastructure are especially vulnerable to aggressive crawling.
Server administrators can block crawlers that behave poorly. If your crawler gets added to a blocklist, you lose access to valuable data sources. Major search engines like Google maintain their reputation by crawling politely and respecting crawl budget allocations, and custom crawlers should follow the same standards.
Core Politeness Rules
The first rule is obeying robots.txt files. These files, placed in website root directories, specify which parts of a site crawlers can access and may include crawl-delay directives. Ignoring robots.txt is the fastest way to get blocked.
Request spacing prevents server overload. Most implementations use delays of 10-15 seconds between requests to the same domain. Popular sites with robust infrastructure can handle faster crawling, while smaller sites need longer delays.
Server response monitoring provides real-time feedback. If a server takes longer to respond or returns error codes, polite crawlers automatically slow down or pause. This adaptive behavior protects struggling servers from additional load.
Calculating Crawl Delays
| Factor | Impact on Delay |
|---|---|
| Domain Size | Larger sites = shorter delays (5-10 sec) |
| Server Response Time | Slow responses = longer delays |
| Robots.txt Directive | Always honored if specified |
| Error Rates | Multiple errors = extended pause |
The crawl delay calculation balances multiple factors. Large, established websites expect crawler traffic and build infrastructure to handle it. Small websites need more breathing room between requests.
Response time directly affects politeness. If a server takes 3 seconds to respond, that signals heavy load. Polite crawlers increase their delay accordingly, often using exponential backoff when problems persist.
Warning Signs Your Crawler Needs Adjustment
Consecutive HTTP 500+ errors indicate your crawler is causing problems. After five straight server errors or timeouts, pause crawling for several hours. The server is either overloaded or your requests are triggering issues.
Complaints from website administrators mean immediate action is required. Include contact information in your crawler’s user-agent string so admins can reach you. Many will ask for changes before blocking your crawler entirely.
Best Practices
Set a minimum delay of 0.1 seconds between requests, even for large sites. This prevents accidental denial-of-service conditions. Set a maximum delay of 2 minutes to keep your crawler from stalling indefinitely.
Use descriptive user-agent strings that identify your crawler and provide contact information. Transparency helps website administrators understand your crawler’s purpose and reach you if issues arise. Anonymous crawlers are more likely to face blocking.
Monitor and log all HTTP status codes. Tracking response patterns helps you identify when politeness rules need adjustment. Keep records of which domains require special handling.
Key Takeaways
Polite crawling protects both websites and your crawler’s access to data. The standard approach includes 10-15 second delays between requests, strict robots.txt compliance, and server response monitoring. Smaller domains need longer delays, while large sites can handle faster requests.
Ignoring politeness rules leads to IP blocking, legal complaints, and damaged reputation. Build adaptive delays that increase when servers show signs of stress. Include contact information in your user-agent string to resolve issues before they escalate.
The investment in polite crawling pays off through sustained access and good relationships with website operators. Respect for server resources is not just ethical but practical for long-term data collection success.
Learn more: Building a Polite Web Crawler, Web Crawler Politeness Policy
data from the web