HTTP Headers for Web Scraping

Businesses benefit from collecting data and monitoring their competitors, which they often do through web scraping. While web scraping is crucial in making data-driven decisions, it can also be challenging. Improper use might cause you to get your IP address blocked or receive poor-quality data.

There are many ways to optimize scraping operations. An often overlooked one is using HTTP headers. We will cover all you need to know about them.

What are HTTP Headers?

HTTP (or The Hypertext Transfer Protocol) is the foundation of the internet which provides a standardized way for devices to communicate with each other while transferring data. It defines how the client's (e.g., a browser) data request is constructed and how the server needs to respond.

HTTP headers are invisible to end-users but are a part of every online data exchange. They enable the client and the server to send additional information within the request or a response. The data is organized according to HTTP headers, of which we can distinguish two primary types:

• Request header informs about the requested data or the client. For example, request headers can indicate the format of data the client needs.
• Response headers carry information about the response or the server. For example, a response header can indicate the format of the data server returns.

Besides enabling communication, HTTP headers bring various other benefits such as optimizing performance, providing multilingual content, helping troubleshoot connection problems and increasing security. For web servers, the latter means restricting bot-like actions which can overload the server. Unfortunately, web scraping gets lumped in together with bots, meaning bans are frequent.

What is the role of HTTP Headers in Web Scraping?

HTTP headers are essential in ensuring a smooth browsing experience for ordinary users. They inform the server what device is connecting to it and what data is needed. Therefore, looking for suspicious HTTP headers and blocking the related IPs is one of the most popular anti-scraping measures.

If you want your web scraper to blend in and avoid blocks, HTTP headers must appear as if coming from regular internet users. Any issues or discrepancies can arouse suspicion, and the server may suspect that you are using a bot.

HTTP headers may also help you take a step further and mask your bot as a new user for some requests. Sending too many of them as one user will alarm the server, so you should rotate between multiple request headers that don't stand out from the rest.

HTTP headers also play a crucial role in defining the quality of data you retrieve. Incorrectly setting them up may result in poor data quality or a significant increase in the traffic needed for web scraping.

To put it shortly, optimizing the most important headers decreases the chances of IP blocks and increases data quality. Since there are so many HTTP headers, you do not need to know them all - it is enough to start with the most relevant ones for web scraping.

What are the most important HTTP Headers for Web Scraping?

User-Agent header

The User-Agent request header informs the server what browser and operating system version the client is using. Such information helps the server to decide what layout to use and how to present data. It is the first obstacle you must bypass because websites filter requests for uncommon User-Agent headers.

The most frequent mistake here is sending too many requests with the same User-Agent HTTP header. It raises suspicion for the server because regular internet users don’t send as many requests as bots do. Make sure to imitate multiple regular User-Agent headers and use the most popular ones to blend in.

User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:100.0) Gecko/20100101 Firefox/100.0

Referer header

The referrer header informs the web server about the last web page visited before sending the request. Regular users rarely jump randomly to websites on the internet. Instead, they move from one website (e.g., a search engine) to another. Such actions are reflected in the referer header.

It is an important but often overlooked HTTP header that allows imitating users better. Your scraper bot should reflect a reputable website as a source. Using a popular search engine could be a great option.

Referer: http://www.google.com/

Cookie header

The cookie HTTP header includes stored cookies. The server sends these small blocks of data to the client and expects them back with the next request. Cookies enable the server to identify users and remember their actions (for example, log-in information or the content of a shopping cart).

Visitors' privacy settings can block the cookie header, so it is optional. However, cookies are still advantageous when web scraping. If you use them correctly, you can mimic regular user behavior better or tell the server that you are a new user. Not using cookies properly might raise some red flags for the server.

Cookie: sessionToken=123abc

Accept-language header

Accept-Language header informs the web server about the language client prefers. This HTTP header is used to set the language of the webpage if the server can't do it by other means, such as URL addresses or IP address location.

Therefore, the accept-language header should align with all other information while web scraping. When it doesn't correspond to the IP or requested language in the URL, you risk your scraper bot getting banned. In addition, the Accept-Language header can help you appear as a local visitor better.

Accept-Language: en-US

Accept header

Accept request header notifies the web server about the media type the client expects and can understand. The client provides available text, image or video types, and the server uses content negotiation to select one.

Choosing a suitable media type and ensuring a swift process makes for faster communication and better data delivery. Additionally, submitting unusual accept headers might arouse suspicion.

Accept: text/html, image/jxr

Accept-Encoding header

The Accept-Encoding request header informs the web server of the acceptable data format. In particular, what compression algorithm should be used when sending the data from the web server to the client. Usually, it's a popular format such as gzip or Brotli.

When the server compresses the data, it can use less traffic, and the client can receive data faster. However, web servers aren't always able to compress files, but you should still use this HTTP header to increase the quality of the data you get while web scraping.

Accept-Encoding: gzip

Host header

The host HTTP header tells the target server's domain name and port number. If the port number is missing, the default one is used (HTTP URLs use 80). Additionally, the host header is mandatory for all HTTP/1.1 requests.

When there is no host header, or if it contains more than one host, your connection will be unsuccessful. Access will also be denied if this header is incorrect. Luckily, nowadays the header is almost always configured automatically, so leaving it be is enough. You can try tinkering with it, though.

Host: metrow.com

Conclusion

Optimizing HTTP headers will surely improve your web scraping process, and you can start with the ones we mentioned here. Just remember that it is only a part of the puzzle. Other tools, such as proxies for web scraping, are equally necessary. With the right steps, no data will be out of your reach.