| name | flutter-mcp |
| description | Use this skill whenever inspecting, interacting with, or live-editing a running Flutter app via the Flutter MCP toolkit server (`mcpServers` key **`flutter-mcp-toolkit`**, or legacy **`flutter-inspector`**). Covers preflight, snapshot/tap/enter/scroll loop, hot-reload validation, and error envelope parsing. |
Flutter MCP
Golden path for agents driving a live Flutter app via the flutter-mcp-toolkit MCP server entry. Older configs may use the legacy flutter-inspector mcpServers registry id for the same binary (that id is not the Claude subagent flutter-mcp-toolkit-runtime).
When to use
- User references a running Flutter app (debug mode) and wants to inspect, screenshot, interact with, or hot-reload it.
- User pastes a VM service URI (
ws://127.0.0.1:8181/.../ws) or mentions port 8181.
- You need runtime proof (before/after screenshots) that a code edit took effect.
Preflight (always first)
Before any VM-dependent call:
- Call
doctor (or run flutter-mcp-toolkit doctor --json) — parses env, ports, app reachability.
- Confirm required toolkit extensions exist on the target:
ext.mcp.toolkit.app_errorsext.mcp.toolkit.view_detailsext.mcp.toolkit.view_screenshotsext.mcp.toolkit.inspect_widget_at_point
If missing, stop and report the instrumentation gap — do not guess:
- Add
mcp_toolkit to pubspec.yaml.
- Ensure
MCPToolkitBinding.instance..initialize()..initializeFlutterToolkit(); runs before runApp.
- Hot restart (not reload) — reload is often insufficient for extension registration.
Tool naming (v3.0.0+)
All MCP tools surface under the fmt_ capability prefix
(fmt_tap_widget, fmt_hot_reload_and_capture, etc.). The prefix is
mandatory in tools/call. Skill-local references below use the bare name
for readability — when invoking, prepend fmt_. Dynamic-registry host
tools (fmt_list_client_tools_and_resources, fmt_client_tool,
fmt_client_resource) use the same prefix for a single consistent surface.
Interaction loop (Playwright-style)
fmt_semantic_snapshot → returns s_0..s_N refs + snapshot_id.fmt_tap_widget / fmt_enter_text / fmt_scroll / fmt_swipe / fmt_long_press / fmt_drag — act on a ref. Always pass snapshotId — you get a structured stale_snapshot error if the tree moved, instead of a silent wrong tap.fmt_evaluate_dart_expression — read state directly (e.g. AgentState.instance.counter).fmt_hot_reload_and_capture — after a code edit, returns reload status + screenshot + fresh snapshot + errors in one response. Prefer this over manual reload + separate capture.
Error envelope contract
Errors are {code, message, details, descriptor, recovery}. Parse error.descriptor (not the top-level object) for the machine-readable shape. Strict schemas default to additionalProperties: false — unknown params reject.
Common codes and recovery:
connection_selection_required — retry with arguments.connection.targetId or exact arguments.connection.uri from app.debugPort.wsUri.target_not_found — refresh targets, then prefer exact arguments.connection.uri.stale_snapshot — call fmt_semantic_snapshot again, then retry the action with the new snapshot_id.tool_not_found — confirm the prefixed name (fmt_<tool>); v3.0.0 dropped legacy unprefixed names.- Empty screenshot output — verify the server was not started with
--no-images.
- Missing view resource/tool — verify the server was not started with
--no-resources.
Visual QA
- Before/after screenshots are the proof artifact for any UI claim. Capture before with
fmt_capture_ui_snapshot (or one of the visual://localhost/... resources), edit, fmt_hot_reload_and_capture, compare.
- For each reported visual issue, attach coordinate +
fmt_inspect_widget_at_point output.
- Map defects to source via
fmt_get_app_errors top stack frame (file, line, column) when available.
- Do not use
fmt_debug_dump_* unless explicitly requested (server must be started with --dumps; high token cost).
Permissions (macOS)
Screen Recording permission belongs to the process running flutter-mcp-toolkit (or the MCP server host). If visual capture is denied:
flutter-mcp-toolkit permissions status
flutter-mcp-toolkit permissions request
flutter-mcp-toolkit permissions open-settings
Non-modifiable apps
If the target app cannot be instrumented (third-party binary, restricted env), report flutter-mcp as unavailable for that app. Do not claim screenshot/layout/error inspection success.
Related
- For the dynamic-tools side (registering custom MCP tools from inside the Flutter app), see the
flutter-mcp-toolkit-custom-tools skill.
- For routing across setup / inspect / control / debug skills, see
flutter-mcp-toolkit-guide.
