Flutter MCP Toolkit Inspect

When to use

Use this skill for read-only state inspection of a running Flutter app: what is shown on screen, recent errors, available debug targets, VM metadata, and widget tree details. Do not use for driving interaction — that is the interact skill. Start with discover_debug_apps when no connection target is established. Start with semantic_snapshot when you need to know which widgets are on screen.

Recipes

Fast inspect cycle (prefer batch)

flutter-mcp-toolkit batch --steps '[
  {"name":"semantic_snapshot"},
  {"name":"get_app_errors","args":{"count":5}},
  {"name":"get_screenshots","args":{"mode":"flutter_layer","compress":true}}
]'

Use mode: flutter_layer on get_screenshots on macOS to avoid Screen Recording permission failures. capture_ui_snapshot uses the separate screenshotMode field.

Snapshot the visible UI

1. Call semantic_snapshot().
2. Read interactionSurface: flutter_widgets (tap-by-ref works), hybrid (sparse semantics), game_canvas (use evaluate_dart_expression + screenshots).
3. Each interactive node has a stable ref (s_0, s_1, …) and the response includes a snapshot_id.
4. Pass refs to interaction tools; pass the snapshot_id value as snapshotId to detect staleness.

After a code edit

Prefer hot_reload_and_capture over separate reload + snapshot + screenshot calls.

Find an error by message

1. Call get_app_errors(count: 10).
2. Inspect the errors array — each entry has message, stack trace, and timestamp.
3. Match on message text to find the source.

List debug-mode apps

1. Call discover_debug_apps().
2. Read the targetId (canonical WebSocket URI) for each active target.
3. Pass the chosen URI as connection.targetId on subsequent tool calls.

Get widget at coordinates

1. Call inspect_widget_at_point(x: 200, y: 400).
2. The response identifies the deepest widget and render node at those global logical pixel coordinates.

Save a screenshot to a file

1. Call get_screenshots().
2. If meta.fileUrls is non-empty, screenshots are on disk at those paths. Otherwise the response contains base64 ImageContent blocks — extract and write manually.
3. To force file output, configure an images output directory on the server before calling.

Tool reference

discover_debug_apps

List all active Flutter debug targets with canonical WebSocket URIs.

• connection (object, optional) — accepted by schema, ignored by executor; discovery is always local.

discover_debug_apps()

Returns: {"targets": [{"targetId": "ws://127.0.0.1:8181/<token>/ws", "host": "...", "port": 8181}]}

• vm_service_unavailable — no debug-mode Flutter process found.
• tool_not_found — binary predates v3.0.0; run make build.

get_app_errors

Retrieve the most recent application errors from the Dart VM.

• count (integer, optional, default: 4) — number of errors to return.
• connection (object, optional) — connection override.

get_app_errors(count: 5)

Returns: {"message": "2 errors found", "errors": [{"message": "...", "stack": "..."}]}

• vm_service_unavailable — app not reachable.
• connection_selection_required — multiple targets; supply connection.targetId.

get_screenshots

Capture screenshots of all views.

• compress (boolean, optional, default: true) — compress PNG output.
• mode (string, optional, default: auto) — auto, flutter_layer, or desktop_window.
• permissionPolicy (string, optional, default: check_only) — check_only, auto_request_once, or request_always.
• connection (object, optional) — connection override.

get_screenshots(mode: "flutter_layer", compress: false)

Returns: ImageContent blocks (base64 PNG) when no output dir configured, or TextContent URL refs + meta.fileUrls when file output is enabled.

• permission_denied — retry with permissionPolicy: "auto_request_once".
• vm_service_unavailable — app not reachable.

get_view_details

Get dimensions, device pixel ratio, and display ID for all views.

• connection (object, optional) — connection override.

get_view_details()

Returns: {"views": [{"id": 0, "width": 1280, "height": 800, "devicePixelRatio": 2.0}]}

• vm_service_unavailable — app not running.
• connection_selection_required — multiple targets; supply connection.targetId.

get_vm

Return Dart VM metadata: version, isolates list, pid, and architecture.

• connection (object, optional) — connection override.

get_vm()

Returns: {"type": "VM", "name": "vm", "version": "3.x.x", "isolates": [...]}

• vm_service_unavailable — app not reachable.
• connection_selection_required — multiple targets active.

get_extension_rpcs

List all registered VM service extension RPCs in the running app.

• isolateId (string, optional) — schema-declared but not read by executor; checks all isolates when omitted.
• isRawResponse (boolean, optional) — schema-declared but not read by executor.
• connection (object, optional) — connection override.

get_extension_rpcs()

Returns: {"extensionRPCs": ["ext.flutter.inspector.getRootWidget", "ext.mcp.toolkit.semantic_snapshot"]}

• vm_service_unavailable — app not running.
• connection_selection_required — multiple targets.

semantic_snapshot

Return a compact accessibility tree of interactive widgets with stable ref strings and a snapshot_id. A node is listed when it reads (label, value), acts (button, text field, tap, scroll…) or carries a Semantics(identifier:).

• identifierPrefix (string, optional) — keep only nodes whose identifier starts with it ("nav." for one rail).
• subtreeOf (string, optional) — keep one node and its descendants; a ref from the latest snapshot or an identifier, the ref tried first.
• fields (array of strings, optional) — node keys to return; ref is always kept. Names: ref id type identifier label value hint enabled focused checked toggled selected bounds actions children visibleInViewport centerInViewport center.
• connection (object, optional) — connection override.

The tree is always walked whole, so a ref read off a filtered snapshot is the same ref the full snapshot would give and works with every interaction tool. A filtered reply adds totalNodeCount and echoes filter; children lists kept refs only.

semantic_snapshot()
semantic_snapshot(identifierPrefix: "nav.", fields: ["identifier", "selected"])
semantic_snapshot(subtreeOf: "panel.tabs")

Returns: {"snapshot_id": 3, "nodeCount": 1, "viewport": {...}, "nodes": [{"ref": "s_0", "label": "Increment", "actions": ["tap"], "bounds": {...}, "visibleInViewport": true, "centerInViewport": true, "center": {...}}]} — the viewport is stated once in the envelope, not on each node.

• subtree_root_not_found — subtreeOf is neither a ref of the latest snapshot nor an identifier in the tree; no snapshot was taken, refs and snapshot_id are unchanged.
• unknown_field — a name in fields is not a node key; acceptedFields lists them. Over MCP and the CLI the name is refused at the boundary instead — an invalid fields argument naming the accepted keys, without spending a call on the app.
• vm_service_unavailable — app not running or MCPToolkitBinding.initialize() not called.
• connection_selection_required — multiple targets; supply connection.targetId.

inspect_widget_at_point

Identify the deepest widget and render node at a global logical coordinate.

• x (integer, required) — global logical X coordinate.
• y (integer, required) — global logical Y coordinate.
• viewId (integer, optional) — FlutterView ID for multi-view apps.
• connection (object, optional) — connection override.

inspect_widget_at_point(x: 200, y: 400)

Returns: {"widget": {"type": "ElevatedButton", "rect": {"left": 180, "top": 380, "right": 280, "bottom": 420}}}

• vm_service_unavailable — app not reachable.
• invalid_argument — coordinates out of view bounds.

capture_ui_snapshot

Capture screenshots, view details, and app errors in one bundled response.

• errorsCount (integer, optional, default: 4) — errors to include.
• compress (boolean, optional, default: true) — compress screenshots.
• includeViewDetails (boolean, optional, default: true) — include view data.
• includeErrors (boolean, optional, default: true) — include app errors.
• screenshotMode (string, optional, default: auto) — auto, flutter_layer, or desktop_window.
• permissionPolicy (string, optional, default: check_only) — check_only, auto_request_once, or request_always.
• connection (object, optional) — connection override.

capture_ui_snapshot(errorsCount: 2, includeViewDetails: false)

Returns: a TextContent JSON block with screenshots, viewDetails, and errors keys. When screenshots.images contains inline base64, each payload is lifted into a sibling image block and the JSON reports screenshots.imagesDeliveredAs: "image_blocks"; the emptied images list is then the normal shape, not a failed capture. Captures delivered through screenshots.fileUrls stay in the JSON and produce no image blocks.

• vm_service_unavailable — app not running.
• permission_denied — retry with permissionPolicy: "auto_request_once".

connect_debug_app

Explicitly select and connect to a Flutter debug VM target. Use when multiple apps are running or to pin a specific target for the session.

• connection (object, optional) — pass connection.targetId with a WebSocket URI from discover_debug_apps.

connect_debug_app(connection: {targetId: "ws://127.0.0.1:8181/<token>/ws"})

Returns: {"connected": true, "targetId": "ws://127.0.0.1:8181/<token>/ws", "isolates": [...]}

• target_not_found — URI doesn't match a running app; re-run discover_debug_apps for the exact URI.
• connection_failed — VM refused connection; verify the app is still running in debug mode.