Output Formats

Output formats

analyze and the instrumented app write JSON Lines: one self-contained JSON object per line. The field names and types below come from the toJson methods in lib/src/features/*/data/models/. Extracted Features explains how each static metric is calculated.

Static analysis JSONL (analyze)

One JSON object is written for each rebuild scope: a State subclass, a ConsumerWidget/HookConsumerWidget, or the builder callback of a state-management widget (BlocBuilder, Consumer, Obx, …). The analyze output contains exactly these 18 fields (AnalysisResultModel.toJson):

{
  "instanceId": "42",
  "filePath": "lib/screens/shopping_cart_screen.dart",
  "scopeName": "_ShoppingCartScreenState",
  "scopeType": "State",
  "treeNonConstWidgetCount": 24,
  "treeMaxWidgetNestingDepth": 7,
  "treeListRenderingStrategy": 2,
  "rootBuildReturnsConstWidget": 0,
  "treeConstWidgetCount": 2,
  "helperReferenceCount": 2,
  "usesLayoutDependentBuilder": 1,
  "treeCyclomaticComplexity": 5,
  "treeIterationCount": 1,
  "treeMaxIterationNestingDepth": 1,
  "iterationWidgetCount": 3,
  "valueObjectAllocCount": 4,
  "helperWidgetCount": 3,
  "helperMaxWidgetNestingDepth": 2
}

Field reference

Field	Type	Description
instanceId	string	ID for this scope: hash of the root-relative path plus the scope name (and, for non-State scopes, its type and occurrence index). Used to join with runtime profiler data. It is not unique across transplanted targets that share one file/class, so the benchmark pipeline keys by sample_id instead.
filePath	string	Source path relative to the analyzed project root.
scopeName	string	Class name of the scope, or <Widget>_builder for a builder callback (e.g. BlocBuilder_builder). (Named stateClassName before rebuild-scope support.)
scopeType	string	Kind of rebuild scope: State, ConsumerWidget, or the builder widget name (BlocBuilder, BlocSelector, BlocConsumer, Consumer, Selector, Obx, GetX, GetBuilder, Observer).
treeNonConstWidgetCount	int	Non-const widget instantiations across reachable build bodies; excludes const boundaries and helper-body widgets.
treeMaxWidgetNestingDepth	int	Maximum widget depth composed across reachable custom-widget build bodies.
treeListRenderingStrategy	0/1/2	Worst list-rendering form across builds and helpers: 0 none, 1 lazy (.builder/.separated/.custom/.useDelegate, or a list that is lazy by contract), 2 eager O(N) (concrete children: on a scroll list, a SliverChildListDelegate, or runtime-length Column/Row/Wrap/Flex children). Scroll lists are ListView, GridView, ReorderableListView, PageView, ListWheelScrollView. (Replaced the buildUsesListViewBuilder boolean on 2026-07-20; widened beyond ListView/GridView/slivers on 2026-08-15.)
rootBuildReturnsConstWidget	0/1	Whether every top-level return of the root State.build is a const widget. (Any one const return set it before 2026-08-15.)
treeConstWidgetCount	int	Const widget boundaries across reachable build bodies and helper bodies alike. (Named constConstructorRatio in JSONL produced before 2026-07-18; helper-body const widgets went to helperWidgetCount before 2026-08-15.)
helperReferenceCount	int	Widget-returning helper reference sites in reachable build bodies: invocations, tear-offs, and explicit getters. Helpers returning List<Widget> count; SDK pass-throughs such as toList do not.
usesLayoutDependentBuilder	0/1	Whether builds or helpers use LayoutBuilder, CustomMultiChildLayout, or Flow.
treeCyclomaticComplexity	int	Complexity summed across reachable build bodies, plus helper-body decision points without extra helper base points.
treeIterationCount	int	Loops, collection-for elements, linear collection operations, and List.generate across build and helper bodies.
treeMaxIterationNestingDepth	int	Maximum lexical iteration nesting within any analyzed build or helper body.
iterationWidgetCount	int	Non-const widgets built in per-element scopes across builds and helpers: loops, collection-op callbacks, List.generate, and lazy builders. Includes widgets built by a local function called from inside such a scope.
valueObjectAllocCount	int	All non-const, non-widget constructor allocations across build and helper bodies.
helperWidgetCount	int	Non-const widget instantiations in reachable helper bodies; const ones are counted by treeConstWidgetCount. (Included const widgets before 2026-08-15.)
helperMaxWidgetNestingDepth	int	Maximum widget nesting within any individual reachable helper body.

0/1 fields are Dart bools serialized as 1/0 by toJson. See Extracted Features for the precise definition of each metric.

Key migration (2026-07-20 rename)

Feature keys were renamed so every name states its scope: tree* = aggregated over the whole static call tree, root* = root build() only, helper* = helper bodies only. Older JSONL files can be normalized with this map:

Old key (pre-2026-07-20)	Current key
buildWidgetInstanceCount	treeNonConstWidgetCount
buildMaxWidgetNestingDepth	treeMaxWidgetNestingDepth
buildUsesListViewBuilder (bool, pre-07-20) / buildListRenderingStrategy	treeListRenderingStrategy
buildReturnsConstWidget	rootBuildReturnsConstWidget
constConstructorRatio (pre-07-18) / constWidgetCount	treeConstWidgetCount
buildHelperMethodCount	helperReferenceCount
buildCyclomaticComplexity	treeCyclomaticComplexity
buildIterationCount	treeIterationCount
buildMaxIterationNestingDepth	treeMaxIterationNestingDepth
helperMethodWidgetCount	helperWidgetCount
helperMethodMaxNestingDepth	helperMaxWidgetNestingDepth

usesLayoutDependentBuilder, iterationWidgetCount, valueObjectAllocCount, and the identity keys (instanceId, filePath, stateClassName — since renamed to scopeName) are unchanged. The legacy boolean buildUsesListViewBuilder maps onto the none/lazy levels of the ordinal only; it cannot express eager (2).

Rebuild-scope rows

analyze emits one row per rebuild scope, so a file can contribute several overlapping rows: a State row counts the widgets built inside a nested BlocBuilder callback and the callback gets its own row. That is deliberate — a parent rebuild re-runs the callback, while the callback row measures the path its package can rebuild on its own.

Use --scope-types to narrow the output (--scope-types=State reproduces the pre-rebuild-scope rows). inject only instruments State subclasses and skips rows of any other scopeType, so a full-scope JSONL can be passed to it unchanged.

Runtime profiler JSONL (run / instrumented app)

Two event types are emitted, distinguished by the event field. Which one you get depends on the Flutter build mode (see inject): --profile → performance_metric, --debug → dataflow-metric. Every event carries a timestamp (ISO-8601) and the instanceId that joins back to the static-analysis record.

Performance event, emitted under --profile (PerformanceMetricsModel.toJson):

{
  "timestamp": "2026-02-20T10:15:30.123Z",
  "event": "performance_metric",
  "instanceId": "42",
  "buildSpan": 4123
}

Field	Type	Description
timestamp	string	ISO-8601 timestamp of the event.
event	string	Always "performance_metric".
instanceId	string	The instrumented State instance.
buildSpan	int	Build duration of the matched rebuild frame, in microseconds (0 on the 5-second timeout fallback).

Dataflow event, emitted under --debug (DataflowMetricsModel.toJson):

{
  "timestamp": "2026-02-20T10:15:30.456Z",
  "event": "dataflow-metric",
  "instanceId": "42",
  "taintedRebuildCount": 5,
  "totalWidgetCount": 42,
  "maxNestingDepth": 7,
  "taintedRatio": 0.119,
  "opacityRebuildCount": 0,
  "shaderMaskRebuildCount": 0,
  "clipRRectRebuildCount": 1,
  "clipOvalRebuildCount": 0,
  "clipPathRebuildCount": 0,
  "backdropFilterRebuildCount": 0
}

Field	Type	Description
timestamp	string	ISO-8601 timestamp of the event.
event	string	Always "dataflow-metric".
instanceId	string	The instrumented State instance.
taintedRebuildCount	int	Widgets that actually rebuilt as a result of the setState.
totalWidgetCount	int	Total widgets in the analyzed subtree.
maxNestingDepth	int	Maximum nesting depth of the analyzed subtree.
taintedRatio	double	taintedRebuildCount / totalWidgetCount.
opacityRebuildCount	int	Rebuilt Opacity widgets.
shaderMaskRebuildCount	int	Rebuilt ShaderMask widgets.
clipRRectRebuildCount	int	Rebuilt ClipRRect widgets.
clipOvalRebuildCount	int	Rebuilt ClipOval widgets.
clipPathRebuildCount	int	Rebuilt ClipPath widgets.
backdropFilterRebuildCount	int	Rebuilt BackdropFilter widgets.