---
title: "App shell: glossary: Agent Ready HTML"
description: "App shell defined: A near-empty HTML document whose content is injected by JavaScript after load, typically a single div with id root or app."
canonical: https://agentreadyhtml.com/glossary/app-shell/
site: "Agent Ready HTML"
last_updated: 2026-11-04
section: "Glossary"
---

# App shell: glossary: Agent Ready HTML

> App shell defined: A near-empty HTML document whose content is injected by JavaScript after load, typically a single div with id root or app.

Source: https://agentreadyhtml.com/glossary/app-shell/
Site: Agent Ready HTML
Last reviewed: 2026-11-04

# App shell

In short

A near-empty HTML document whose content is injected by JavaScript after load, typically a single div with id root or app. Example: The guide lists an empty app shell beside a 403 as responses that stop fetch-only agents. Related terms: Hydration, Initial HTML, Rendered HTML, Content negotiation, Answer provenance.

## Source of the example

The example in the summary above is from [vercel.com](https://vercel.com/kb/guide/make-your-site-readable-by-ai-agents), read 4 November 2026.

## Where it shows up on this site

-   [Initial HTML reference](https://agentreadyhtml.com/initial-html/)
-   [The cost of client-side rendering](https://agentreadyhtml.com/client-side-rendering-and-agents/)

## Neighbouring terms

-   [Hydration](https://agentreadyhtml.com/glossary/hydration/): The step where client JavaScript attaches event handlers to server-rendered HTML.
-   [Initial HTML](https://agentreadyhtml.com/glossary/initial-html/): The HTML document a server returns for a URL before any JavaScript runs.
-   [Rendered HTML](https://agentreadyhtml.com/glossary/rendered-html/): The DOM after a browser has run the page scripts.
-   [Content negotiation](https://agentreadyhtml.com/glossary/content-negotiation/): The HTTP mechanism where the client states preferred formats in the Accept header and the server picks a representation for the same URL.
-   [Answer provenance](https://agentreadyhtml.com/glossary/answer-provenance/): Which fetched page an agent answer can be traced to.

## Sources

1.  [vercel.com](https://vercel.com/kb/guide/make-your-site-readable-by-ai-agents) https://vercel.com/kb/guide/make-your-site-readable-by-ai-agents, read 4 November 2026

Last reviewed 4 November 2026

Edition

Crawl

2026-11-04

Page updated

2026-11-04

Method

How the viewer reads a page, how a file is graded and how a platform is scored: [the method page](https://agentreadyhtml.com/method/).