Quickstart

Prerequisites: Dart 3.13 and Flutter 3.47 or newer, and a Flutter project (a plain flutter create output works). dowel comes with crumbs, and crumbs:install scaffolds its harness on the first run.

Install crumbs#

flutter pub add crumbs
dart run crumbs crumbs:install

The installer scaffolds the dowel harness when it is missing, registers crumbs as a dowel plugin and patches lib/main.dart with a kDebugMode block that installs crumbs with the exception and dump watchers. On a Magic app with a magic_devtools release built on crumbs it also wires MagicCrumbsIntegration.install() after Magic.init(); see Installation for every step.

From here on the fast launcher ./bin/dowel runs every command; dart run crumbs <command> is the slower equivalent that needs no build. Confirm the plugin registered:

./bin/dowel list

The output lists the crumbs: namespace.

Start the app and generate traffic#

./bin/dowel start --device=chrome

dowel starts flutter run, records the VM Service URI of the session, and every crumbs:* command and crumbs_* tool dials that session.

Use the app. On a vanilla app, package:logging records fill the log buffer and debugPrint calls the dump buffer; on a Magic app, HTTP calls through the Http facade, model saves, cache reads and gate checks land in their buffers too. To produce records on purpose, from anywhere in the app:

import 'package:flutter/foundation.dart';
import 'package:logging/logging.dart';

void emitSampleRecords() {
  Logger('Quickstart').info('quickstart test log'); // a log record
  debugPrint('quickstart test dump'); // a dump record
}

Read the buffers from the CLI#

./bin/dowel crumbs:tail --level=INFO
./bin/dowel crumbs:dumps
./bin/dowel crumbs:requests --limit=10
./bin/dowel crumbs:clear

Each read command prints the newest records, oldest first (--limit defaults to 50). crumbs:clear empties every buffer, so the next read holds only what happens after it. crumbs:tail --follow keeps printing new log lines until you stop it.

Read the buffers from an agent#

Write the MCP entry and reconnect the client:

dart run crumbs mcp:install

In Claude Code, run /mcp reconnect dowel; the crumbs_* tools appear next to the dowel_* tools. A typical inspection:

crumbs_clear {}
# exercise the feature
crumbs_tail {"level": "WARNING", "limit": 20}
crumbs_requests {}
crumbs_exceptions {}

crumbs_tail returns log records at or above the level, crumbs_requests every captured HTTP request with its status, duration and masked headers, and crumbs_exceptions the uncaught errors with their stack traces. Every tool reads an ext.crumbs.* extension in the running app; the buffers fill passively, so nothing in the app changes between reads.

Related Documentation#

• Installation: manual wiring, the Magic integration and a Dio interceptor.
• Watchers: which watchers are opt-in and how they chain to Sentry and Bugsnag.
• Tool reference: every tool's input and output shape.
• Redaction, File sink and Cursor and filters: mask secrets, keep a timeline on disk, and follow a buffer.