Robots.txt is a text file that represents the Robots Exclusion Protocol. This file is located in the root directory of a website and is the first place that most search engine robots (called crawlers) check when visiting. Its main function is to provide directives and instructions to robots regarding which parts of the website are allowed to be crawled and which should be explicitly excluded.
Conceptually, robots.txt is not a security mechanism, but rather a crawl budget management tool. Through directives such as Disallow and Allow, it allows the webmaster to prevent robots from accessing directories or files that contain duplicate, low-quality, confidential, or purely technical content that does not need to be indexed. This is extremely important to ensure that valuable crawl budget is spent on the most important and strategic pages of the site.
Although robots.txt can disallow crawling, it cannot guarantee complete exclusion from the index. Search engines can index a URL if they find links to it from elsewhere on the web. Therefore, the file is a first line of defense and control, but for complete exclusion from the index (noindex) additional meta directives are required.