# Main Domain and Subdomain Differences **Main Domain Name** Also called a first-level domain name, it has only one dot (point) like `"mysite.com"` (or two dots in the case of [co.jp](/en/faq/tag-and-domain/domain-main-vs-sub.md), ne.jp, etc.). The subdomain name comes before this domain name. **Subdomain Name** A domain name that comes before the main domain name, with multiple dots in the domain name. For example, `"domain.mysite.com"` is a second-level subdomain name. **Third-Level Subdomain Name** Simply add new content before "domain" in cases like `"help.domain.mysite.com"`. N-level subdomain names are added before N-1 level subdomain names. **Directory** Similar to a folder that indicates a location on a computer; it is a path string. `"mysite.com"` is generally considered the root directory of a website, and subdirectories are located under the root directory. Link paths are typically specified by adding "/" at the end of the domain name, like `"www.mysite.com/agent"`. The "/" indicates a subdirectory. **Note:** With Ptengine, you can measure all subdomains and subdirectories under the main domain name by simply adding the main domain name. --- # Agent Instructions: Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter: ``` GET https://helps.ptengine.com/en/faq/tag-and-domain/domain-main-vs-sub.md?ask= ``` The question should be specific, self-contained, and written in natural language. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.