Web Viewer displays local HTML as plain text (not rendered) when using Post Message or asset URL

salvadormigarciahw2r
Wed, 29 Oct 2025 18:57:38 +0000
Issues / Bugs

Hi everyone,
I’m building an app that uses a local html file to reformat and display an API responses in a styled way. The goal is for the HTML file to act as a render layer with the API text sent into it via the Web_Viewer → Post Message block.

Here’s what I’m seeing:

The html file loads in the Web Viewer (it shows up).

However, instead of rendering HTML, the Web Viewer shows the raw HTML source as plain text.

Even when I send messages via the Post Message block, the content updates, but still as literal HTML text (no rendering).

The file contains the proper structure and the thunkableWebviewerExtension.js import for message handling (in case that was needed).

I’m testing this in both Thunkable Live on iOS and Web Preview, same result.

It seems like the Web Viewer isn’t actually evaluating the local HTML file — it’s just printing it.

Has anyone successfully:

Sent HTML content to a local Web Viewer asset and had it render, not print as text?

Used Post Message to inject dynamic HTML into a local file that uses the Thunkable WebViewer extension?

Expected: HTML renders normally (e.g., styled text, line breaks)
Actual: HTML shows as escaped text (e.g., content instead of formatted output)

Has anyone found a reliable workaround (maybe a data:text/html URL or hosted HTML page) to make the Web Viewer actually execute the HTML?

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