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Datasette Apps: Host custom HTML applications inside Datasette

ID

1991

Status

new

Published

19 Jun 2026, 7:58 AM

Fetched

27 Jun 2026, 8:23 PM

Provider

Simon Willison

Category

developer-ai

Original URL

https://simonwillison.net/2026/Jun/18/datasette-apps/

Source URL

https://simonwillison.net/atom/everything/

Excerpt

Today we launched a new plugin for Datasette, datasette-apps, with this launch announcement post on the Datasette project blog. That post has the what, but I'm going to expand on that a little bit here to provide the why. The TL;DR Datasette Apps are self-contained HTML+JavaScript applications that run in a tightly constrained <iframe> sandbox hosted on your Datasette application. They can use JavaScript to run read-only SQL queries against data in Datasette, and can run write queries too if you configure them with some stored queries. Here's a very simple example and a more complex custom timeline example - the latter looks like this: Apps are allowed to run JavaScript and render HTML and CSS. They are limited in terms of access - the <iframe sandbox="allow-scripts allow-forms"> they run in prevents them from accessing cookies or localStorage and they also have an injected CSP header (thanks to this research) which prevents them from making HTTP requests to outside hosts, preventing a malicious or buggy app from exfiltrating private data. Datasette Apps started out as my attempt at building a Claude Artifacts mechanism for Datasette Agent, but I quickly realised that the sandboxed pattern is interesting for way more than just adding custom apps in a chat interface and promoted it to its own top-level concept within the Datasette ecosystem. They're also a fun way to turn my multi-year experiment in vibe-coded HTML tools into a core feature of my main project! You can try out Datasette Apps by signing in with GitHub to the agent.datasette.io demo instance. Why build this? Since the very first release, Datasette has offered a flexible backend for creating custom HTML apps via its JSON API. One of my earliest Datasette projects was an internal search engine for documentation when I worked at Eventbrite - it worked by importing documents from different systems into SQLite on a cron and then serving them through a Datasette instance with a custom HTML+JavaScript search interface that directly queried the Datasette API. I had client-side JavaScript constructing SQL queries, which originally was intended as an engineering joke but turned out to be a really productive way of iterating on the app! That project, combined with my experience building my HTML tools collection and my experiments with Claude Artifacts, has convinced me that adding a Datasette-style backend to a self-contained HTML frontend is an astonishingly powerful combination. Imagine how much more useful Claude Artifacts could be if they had access to a persistent relational database. That's what I'm building with Datasette Apps! Neat ideas in Datasette Apps Here are a few of the ideas and patterns I've figured out building this which I think have staying power. <iframe sandbox="allow-scripts" srcdoc="..."> + <meta http-equiv="Content-Security-Policy" content="default-src 'none'; script-src 'unsafe-inline'; style-src 'unsafe-inline'; img-src data: blob:;"> This is t