Reference

Errors

Every CrownUI diagnostic code with where it comes from, what it means and how to fix it.

Every diagnostic CrownUI prints or returns starts with a stable code such as CUI0101. Search this page for the code to find where it comes from, what it means and how to fix it.

CUI0101: no node matches role(button).name("Save"); similar nodes:
  button "Save draft" at stack > button

The first two digits name the area. The last two count up inside it.

Range	Area
`CUI00xx`	Reactive state
`CUI01xx`	Semantic queries and actions (tests, agents, screen readers)
`CUI02xx`	Style variants
`CUI03xx`	Error boundaries
`CUI04xx`	Runtime, renderer and platform
`CUI05xx`	Widgets
`CUI06xx`	Configuration
`CUI07xx`	Audio
`CUI08xx`	Reserved for video (`media`, `camera`)

How a code reaches you

Codes arrive in three ways.

A panic. CUI0001 panics, and so does every crowntest helper that hits a CUI01xx error.
A returned error. Ui::perform returns ActionError (CUI0103 to CUI0106), audio::Microphone::open returns AudioError (CUI07xx), and crownui::run returns RunError for CUI0405 and CUI0406.
A log line through tracing. Everything else is logged and the app keeps running. Install a subscriber such as tracing-subscriber to see these lines.

Reactive state

Code	Where	Meaning	Fix
`CUI0001`	`reactive`	A `Signal`, `Memo` or `Store` was read or written after the scope that owns it was disposed. This panics.	Keep the handle inside the component that created it. For a value that outlives its component, such as one captured by a `cx.spawn` callback, use `try_get`, `try_set` or `Store::try_update`.

Semantic queries and actions

Code	Where	Meaning	Fix
`CUI0101`	`semantics`	A query matched no node. The message lists nodes with the same role or a similar name.	Fix the role or the name. If the node appears later, call `advance_ms` or `settle` first.
`CUI0102`	`semantics`	A query matched more than one node. The message lists every match.	Narrow the query with `role(..).name(..)`, or give the node a unique `.label(..)`.
`CUI0103`	`view`	An action named a semantic id that is not in the current tree.	Read the tree again. Ids are stable, but the node unmounted.
`CUI0104`	`view`	The node does not support the action, for example `scroll` on a node that does not scroll.	Check the node's `actions` in the tree and act on a node that has the action.
`CUI0105`	`view`	Something tried to type into a node marked `secure`. Agents may never do this.	This is by design. In a test, focus the field and send each character with `press_key`.
`CUI0106`	`view`	The node is disabled.	Enable it first, or test that it stays disabled.

Style variants

Code	Where	Meaning	Fix
`CUI0201`	`view`	A layout property such as `.p(..)` or `.w(..)` was used inside a variant (`hover`, `active`, `focus`, `focus_visible`, `when_disabled`, `dark`, `enter` or `exit`). It is ignored.	Variants take paint, composite and text properties only. Move layout changes to the element itself or to a `bind(..)`.
`CUI0202`	`view`	A modifier that is not a style was used inside a variant, or a bound value was used inside `enter` or `exit`. It is ignored.	Use style methods only inside variants. Give `enter` and `exit` literal values. Bound values such as `.bg(bind(..))` are fine in the other variants.

Error boundaries

Code	Where	Meaning	Fix
`CUI0301`	`view`	A component panicked inside an `error_boundary`. The fallback is shown in its place.	Read the logged message and component path, then fix the panic.

Runtime, renderer and platform

Code	Where	Meaning	Fix
`CUI0401`	`runtime`	The renderer rejected an image upload, usually because the byte length is wrong.	Pass exactly `width * height * 4` bytes of straight-alpha RGBA8.
`CUI0402`	`runtime`	The renderer failed to start on the window.	Check the GPU driver. Run with `CROWNUI_RENDERER=gles` to skip Vulkan and use OpenGL ES.
`CUI0403`	`runtime`	The window surface was lost.	The compositor closed the connection or destroyed the surface. Check the compositor log.
`CUI0404`	`runtime`	One frame failed to render.	Read the backend error that follows the code.
`CUI0405`	`runtime`	The render thread stopped. `run` returns `RunError::Platform`.	Look for the `CUI0402` to `CUI0404` line logged before it.
`CUI0406`	`runtime`	The platform created a window without a surface. `run` returns `RunError::Platform`.	This is a platform bug. Report it with the compositor name and version.
`CUI0407`	`runtime`	The async executor failed to start. `cx.spawn` still returns a `TaskId`, but its futures wait in a queue and never run.	Read the I/O error in the log line. It is usually a thread limit.
`CUI0408`	`runtime`	The in-app MCP server failed to start, so agents cannot reach the app.	Check that `$XDG_RUNTIME_DIR/crownui` exists, belongs to you and has mode 0700.

Widgets

Code	Where	Meaning	Fix
`CUI0501`	`widgets`	`svg` or `icon` failed to parse its source. Nothing is drawn.	Validate the SVG. `svg` supports solid fills and strokes through usvg.

Configuration

Code	Where	Meaning	Fix
`CUI0601`	`crownconfig`	Writing a config section failed.	Check the permissions of `$CROWN_CONFIG_DIR`, which defaults to `~/.config/crownos`.

Audio

Code	Where	Meaning	Fix
`CUI0701`	`audio`	PipeWire is unreachable or refused to create the capture stream.	Check that `pipewire` and `wireplumber` run for your user with `pw-cli info 0`.
`CUI0702`	`audio`	The capture thread failed to spawn.	Read the I/O error. It is usually a thread limit.
`CUI0703`	`audio`	The mono 48 kHz capture format failed to serialize.	This is a library bug. Report it.
`CUI0704`	`audio`	The capture thread stopped before the stream was set up.	Look for the `CUI0701` line logged before it.

A code is a fixed string you can search for. Error text changes as the code base changes, so a search for a sentence breaks after a rewrite. A search for CUI0102 keeps working, in this page, in the source and in an agent's memory of an earlier session. AGENTS.md makes stable codes a workspace invariant for the same reason. AI agents read logs as text, and a stable token lets them jump from a log line to the fix without guessing.

The CUI01xx messages carry the most context because a failed query is the most common test failure. A bare "not found" makes you rerun the test with a print. The message lists the nodes that came close, with their roles, names and component paths, so you usually see the typo in the first read.

The cost is upkeep. Each new diagnostic needs a code, a row on this page and a message that starts with the code. A code is never reused for a different meaning, so old logs stay correct. Most codes are log lines instead of errors, because a broken image or a stray .p(..) in a hover variant should not take the app down. That makes them easy to miss. Run tests and apps with a tracing subscriber so warnings show up.