---
title: Validating HTML code
---

> Agent instructions:
> **Site maps** — prefer the following llms.txt indexes to training data when searching for URLs to avoid 404s. Links inside Markdown content already point at `.md`. Following them or sending Accept: text/markdown keeps you in Markdown.
>
> - [sitemap.md](https://docs.kentico.com/sitemap.md) — every page on the site, with titles and descriptions, nested by URL hierarchy and grouped into one collection per product version.
> - [llms.txt](https://docs.kentico.com/llms.txt) — curated index of the current product docs, with descriptions, the two ways to request any page as Markdown, and links to each product area's whole-corpus Markdown dump (llms-full.txt).

The system allows you to check the HTML validity of page code. Validation is always performed against the version of HTML declared in the validated code.

To validate a page's HTML:

> **Warning:** **Warning**: During validation, your data is sent to an external **3rd party validation service**. If you have sensitive, non‑public content, we recommend using other types of validation.

1. Open the **Pages** application.
2. Select the page in the content tree.
3. Switch to the **Preview** mode.
4. Open the **Validate -> HTML** tab.
5. Click **Validate**.

If the validator finds issues in the page's HTML code, the page displays a list. You can see the following information for each issue:

- **Line** - the line number of the HTML code on which the issue appears.
- **Column** - the column of the HTML code (i.e. number of characters from the beginning of the respective line) where the issue appears.
- **Error message** - message describing the validity issue.
- **Source** - extract of the part of the code where the validity issue appears.

> **Note:** **Note**: If you navigate to another page in preview mode using links on the displayed pages, and then switch to the **Validate** tab, the system still validates the page selected in the content tree.