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Lit DevTools

Changelog

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Version 0.22.0

The Lit DevTools now run in any server. createLitDevtools() serves the panel from your app’s own origin, without Vite or a second port, and docks it in a drawer along the bottom of the page. An Elysia example puts it next to server rendering on Bun, and a forms example shows form-associated elements with :state(). The panel takes its colours, type and code font from the Lit Design System, and agents can read the docs as Markdown. Nothing needs action to upgrade.

Added

  • The Lit DevTools in any server. createLitDevtools() from @oddsquad/vite-plugin-lit/devframe gives a server without Vite (Elysia, Hono, Bun.serve, a SvelteKit or Next.js route) one request handler for the panel, its page script and its RPC on the app’s own origin, with no lit-devtools dev process or second port.
  • The panel docks in the page. With createLitDevtools(), a Lit button in the corner opens the panel in a resizable drawer along the bottom of the page, and picking an element opens it there instead of in another tab. It reopens as you left it; pass dock: false to keep it a tab.
  • An Elysia example, without Vite. A guestbook that Elysia renders on Bun with @lit-labs/ssr, streams, hydrates and keeps live over a WebSocket, with a form that works before it hydrates. It shows the hydration traps to avoid, attaches the standalone Lit DevTools, and builds into a single executable.
  • A forms example. A text field, a switch and a star rating extend one FormControl base class and work in a plain <form>: they submit with FormData, block submit while invalid, reset, and follow a disabled fieldset. Each shows what it is doing as :state() custom states for CSS to style on.
  • Every docs page has a Markdown copy. Append index.md to a page’s address, follow its rel="alternate" link, or send Accept: text/markdown to get the page as Markdown, with Link headers pointing to llms.txt and the sitemap.
  • An agent skill for the plugin. Agents that read Agent Skills Discovery find it at /.well-known/agent-skills/ on the docs site: setup, CSS delivery, hot-patch failures and the DevTools MCP server in one file.
  • A setup prompt for coding agents. The Installation page has a prompt to copy into your agent; it installs the plugin, adds it to the Vite config and registers the types, then lists what it changed.
  • Browser agents can search and read the docs through WebMCP. In a browser with WebMCP, the docs offer search_docs, read_docs_page and open_docs_page tools.

Changed

  • The panel takes the Lit Design System’s theme. Its colours, focus ring, motion and type scale come from the same tokens as the docs, in both colour schemes. Corners stay square; pills, status dots and the Timeline’s layer chips are round.
  • The panel sets code in Lilex. Values, source locations, timings and the Timeline’s lanes use the Lilex monospace instead of the system one.
  • The Updates count no longer looks like an error. The number on the Updates tab is blue instead of red; the orange count on Components still flags Lit warnings.
  • A lighter split between the tree and the details. The divider in the Components view is a hairline that lights up blue under the pointer, and is just as easy to drag.
  • The docs moved to lit-devtools.oddsquad.dev. Links in the DevTools panel, the README and the extension listing point there, and the old oddcelot.github.io/vite-plugin-lit/ addresses redirect.

Fixed

  • A re-created child keeps its own listeners and lookups. When a parent edit makes Lit re-create a child, #private arrow-function listeners and fields the child sets in connectedCallback, such as a form it looks up, stay the new element’s instead of being overwritten by the old one’s.
  • Dark outlines and nulls are legible. In the dark scheme, unchecked switches, inputs and outlined buttons have a visible outline, and null values in the Properties view no longer fade into the background.
  • The ./build and ./astro/* exports have types on JSR. JSR no longer warns that these entry points have no type declarations, and installing the package from JSR types them like the others.