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How to Build a Web Crawler – A Guide for Beginners

Wednesday, August 4, 2021

As a newbie, I built a web crawler and successfully extracted 20k data from the Amazon Career website. Want to know how to set up a crawler and create a database that eventually turns into your asset at no cost? Let's dive right in. 


Table of Contents

What Is A Web Crawler?

Why Do You Need A Web Crawler?

How to Build A Web Crawler as A Beginner?

Final Thoughts



What is a web crawler?

A web crawler is an internet bot that indexes the content of websites. It can automatically extract target information and data from websites and export data into structured formats (list/table/database).


Why do you/enterprises need a web crawler?

Imagine a world without Google Search. How long do you think it will take to get a recipe for chicken nuggets from the Internet? There are 2.5 quintillion bytes of data being created online each day. Without search engines like Google, it will be like looking for a needle in a haystack.

website database

From Hackernoon by Ethan Jarrell


A search engine is a unique kind of web crawler that indexes websites and finds webpages for us. Besides search engines, you can also build a customized web crawler to help you achieve:


1. Content aggregation: it works to compile information on niche subjects from various resources into one single platform. As such, it is necessary to crawl popular websites to fuel your platform in time.

2. Sentiment analysis: it is also called opinion mining. As the name indicates, it is the process to analyze public attitudes towards one product and service. It requires a monotonic set of data to evaluate accurately. A web crawler can extract tweets, reviews, and comments for analysis.

3. Lead generation: Every business needs sales leads. That's how they survive and prosper. Let's say you plan to make a marketing campaign targeting a specific industry. You can scrape email, phone number, and public profiles from an exhibitor or attendee list of Trade Fairs, like attendees of the 2018 Legal Recruiting Summit.


How to build a web crawler as a beginner?

A. Learn to code and write your own scripts

Writing scripts with computer languages is predominantly used by programmers. It can be as powerful as you create it to be. Here is an example of a snippet of bot code.

 scraping with a programming language

 From Kashif Aziz


Web scraping using Python involves three main steps:

1. Send an HTTP request to the URL of the webpage. It responds to your request by returning the content of web pages.

2. Parse the webpage. A parser will create a tree structure of the HTML as the webpages are intertwined and nested together. A tree structure will help the bot follow the paths that we created and navigate through to get the information.

3. Using python library to search the parse tree.

Among the computer languages for a web crawler, Python is easy-to-implement compared to PHP and Java. It still has a steep learning curve that prevents many non-tech professionals from using it. Even though it is an economic solution to write your own, it's still not sustainable with regard to the extended learning cycle within a limited time frame.


However, there is a catch! What if there is a method that can get you the same results without writing a single line of code?


B. Use ready-made web scraping tools

In case you don't want to learn to code, web scraping tools come in handy. There are many options to choose from, but I recommend Octoparse. Download it and try the Amazon Career webpage for starters:


Goal: Build a crawler to extract data about administrative job opportunities including job title, job ID, description, basic qualification, preferred qualification, and page URL.

URL: https://www.amazon.jobs/en/job_categories/administrative-support


1. Open Octoparse and select "Advanced Mode". Enter the above URL to set up a new task.

2. As one can expect, the job listing spans over multiple pages and requires us to click through each one of them. As such, we need to set up pagination so that the crawler can navigate through it. To do this, click the "Next Page" button and choose "Look click single button" from the Tips Panel.

3. As we want to extract details of each list item, we need to create a loop item to click through them. To do this, simply select one job item. Octoparse will work its magic and identify all other similar elements from the page. Choose the "Select all" from the Action Tips Panel, then click on "Loop click each element".

4. Now that we are on the detail page, and we need to tell the crawler where to get the data. In this case, click "Job Title" and select "Extract the text of the selected element" from the Tips Panel. Repeat this step and get "Job ID", "Description," "Basic Qualification", "Preferred Qualification" and the Page URL.

5. Once you finish setting up the extraction fields, click "Start Extraction" to execute.


But what if SaaS software is not your thing?

Most SaaS software requires new users to take a considerable amount of training before thoroughly enjoying their benefits. Luckily, Octoparse has built-in "Task Templates" that cover over 30 websites for starters to grow comfortable at the beginning. These templates allow users to capture the data without task configuration and are extremely beginner-friendly.

As you gain confidence, you can use an AI-powered auto-detect algorithm to build your crawler. It has step-by-step guides to facilitate you to develop your task. For experienced scrapers, "Advanced Mode" will enable you to extract an enterprise-level volume of data. Octoparse also provides rich training materials for you and your employees to get most of the software.


Final thoughts

Writing scripts can be painful as it has high initial and maintenance costs. No single web page is identical, and we need to write a script for every single site. It is not sustainable if you need to crawl many different websites. Besides, websites tend to change layouts and structures after a period of time. As a result, we have to debug and adjust the crawler accordingly. The web scraping tool is more practical for enterprise-level data extraction with fewer efforts and lower costs.

final thoughts

In case you may have difficulties finding a web scraping tool, I have compiled a list of the most popular scraping tools. This video can walk you through to get your device that fits your needs! Feel free to take advantage of it.

5 best web scraping tools


Author: Ashley Ng

Ashley is a data enthusiast and passionate blogger with hands-on experience in web scraping. She focuses on capturing web data and analyzing in a way that empowers companies and businesses with actionable insights. Read her blog here to discover practical tips and applications on web data extraction.


Webスクレイピングについての記事は 公式サイトでも読むことができます。
Artículo en español: Cómo Construir Un Web Rastreador (Crawler) Desde Cero: Una Guía para Principiantes
También puede leer artículos de web scraping en el Website Oficial



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