Undated · last checked 9 Oct 2026: Claude API docs: Web fetch toolVerbatim: 'The web fetch tool currently does not support websites dynamically rendered with JavaScript.' It points to the separate browser-use tool for pages that need rendering. The latest tool version is web_fetch_20260318.
Claude CodeNot supported
Undated · last checked 9 Oct 2026: Claude Code docs: Tools reference, WebFetch tool behaviorDocs say WebFetch 'fetches the page and converts the response to Markdown when the server returns HTML'. There is no rendering step. The docs do not literally say 'no JavaScript'; this reading is inferred from the documented pipeline.
GitHub CopilotSupported (announced)
Published 11 Aug 2026 · last checked 9 Oct 2026: microsoft/vscode: webPageLoader.ts (fetch tool page loader)The VS Code fetch tool used by Copilot Chat loads the page in an offscreen Electron BrowserWindow with webPreferences javascript: true, then pulls content from the accessibility tree. This covers Copilot in VS Code, not necessarily other Copilot surfaces. The date is the file's last commit.
CCBotNot supported
Published 11 Aug 2026 · last checked 9 Oct 2026: Common Crawl FAQVerbatim: 'Currently, JavaScript is not executed and Cookies are not used.' The page has no explicit updated date; 2026-08-11 is the date on the IP-range information it shows.
ApplebotSupported (announced)
Published 4 Sept 2026 · last checked 9 Oct 2026: About Applebot (Apple Support)Verbatim: 'Applebot may render the content of your website within a browser. If javascript, CSS, and other resources are blocked via robots.txt, it may not be able to render the content properly.'
The extension fetches the page’s HTML as the server sends it and measures the
visible text in it, ignoring scripts and styles. It also looks for an <h1>.
If the raw HTML has at least 500 characters of text, the page has enough
server-rendered content and the result depends only on whether an <h1> is
present.
If the raw HTML has less than that, a short page is not automatically a
problem. The extension compares the raw text with the text on the rendered page
in your browser. The page counts as depending on JavaScript when the rendered
page has at least 500 characters and more than twice the text of the raw HTML.
Results
Status
When
Pass
The raw HTML has at least 500 characters of text and an <h1>
Warn
The raw HTML has at least 500 characters of text but no <h1>
Warn
The page has little text either way, raw or rendered
Fail
The rendered page has at least 500 characters and more than twice the raw HTML’s text
Unmeasured
The HTML could not be fetched, or the raw HTML is thin and the rendered page could not be read to compare it
How to fix
Render the page’s content on the server, so it is in the HTML response rather
than added by scripts after load. Most frameworks support this through
server-side rendering or static generation (for example Next.js, Nuxt, Astro, or
SvelteKit with SSR or prerendering turned on).
Give the page a single <h1> that names what it is about, and enough text for
an agent to tell what the page is for. An <h1> and a few hundred characters is
a reasonable minimum.
You can see what an agent sees by fetching the page without a browser:
curl-s https://example.com/page |less
If the content you expect is missing from that output, agents cannot read it
either.
Support by agent and browser
Announced means the vendor’s own docs or announcement say so. Published is the date on the vendor’s own page, where it has one. Checked is the last time our weekly research found that page still saying so.
Agent
Status
Source
AI assistants
Claude Anthropic
Not supported
noClaude API docs: Web fetch toolUndated · Checked Verbatim: 'The web fetch tool currently does not support websites dynamically rendered with JavaScript.' It points to the separate browser-use tool for pages that need rendering. The latest tool version is web_fetch_20260318.
Coding agents
Claude Code Anthropic
Not supported
noClaude Code docs: Tools reference, WebFetch tool behaviorUndated · Checked Docs say WebFetch 'fetches the page and converts the response to Markdown when the server returns HTML'. There is no rendering step. The docs do not literally say 'no JavaScript'; this reading is inferred from the documented pipeline.
GitHub Copilot GitHub
Supported (announced)
microsoft/vscode: webPageLoader.ts (fetch tool page loader)Published · Checked The VS Code fetch tool used by Copilot Chat loads the page in an offscreen Electron BrowserWindow with webPreferences javascript: true, then pulls content from the accessibility tree. This covers Copilot in VS Code, not necessarily other Copilot surfaces. The date is the file's last commit.
AI crawlers
CCBot Common Crawl
Not supported
noCommon Crawl FAQPublished · Checked Verbatim: 'Currently, JavaScript is not executed and Cookies are not used.' The page has no explicit updated date; 2026-08-11 is the date on the IP-range information it shows.
Applebot Apple
Supported (announced)
About Applebot (Apple Support)Published · Checked Verbatim: 'Applebot may render the content of your website within a browser. If javascript, CSS, and other resources are blocked via robots.txt, it may not be able to render the content properly.'
No evidence yet18
ChatGPT
Gemini
Perplexity
Copilot
Meta AI
ChatGPT Atlas
Comet
Dia
Gemini in Chrome
Edge Copilot Mode
Cursor
Codex
Windsurf
Amazonbot
Bytespider
Cohere
Mistral
DuckAssist
Not applicable4
Browsers show pages to a person after running their JavaScript, and don't read pages on their own, so whether the content is in the server's HTML makes no difference to them.
Chrome
Edge
Firefox
Safari
Names and marks belong to their owners and are used only to identify products. None of these vendors is affiliated with Sitebulb. Spotted something out of date? Send a correction.
Adoption on the top 100 sites
94%
79 of 84 measured sites implement it
Scanned 23 Oct 2026 with the Sitebulb Labs extension, against the Tranco list (tranco-56Z8N). 16 sites couldn’t be measured (bot challenge or timeout) and are left out of the share.
8 or more points is Established, 5 to 7 is Gaining traction, 2 to 4 is Speculative and under 2 is Stalled. A feature is also Stalled when more vendors have said no than yes. Read the spec.
Community insights
Mixed
OAI-SearchBot (search) and GPTBot (training) stopped just fetching HTML and started running JavaScript and rendering pages.
So over a year later, AI Search platforms still cannot render JavaScript-based content. Therefore, I would still be very careful with how you leverage JavaScript-based content on your site.
The data indicates that while ChatGPT and Claude crawlers do fetch JavaScript files (ChatGPT: 11.50%, Claude: 23.84% of requests), they don’t execute them. They can’t read client-side rendered content.
Hisashi SpaceDeveloper of @SOHOOn their blog, 30 Sept 2026XWebsite
Glenn GabeSEO consultant, G-Squared InteractiveOn their blog, 19 Oct 2026XBlueskyWebsite
Giacomo ZecchiniR&D Director, MERJOn their blog, 17 Dec 2024X