| name | profile-dart-code |
| description | Profile Dart command-line applications using the VM Service protocol to
capture CPU samples and identify performance bottlenecks. Helps agents
automate CPU profiling, generate function call breakdown summaries, and
export JSON profiles without a browser or DevTools. |
| key_features | ["Automated VM Service WebSocket connection","CPU sampling and top-function call summary","JSON trace export for further analysis"] |
Dart CPU Profiling
Guidelines and automated tools for capturing CPU profiles and identifying
bottlenecks in Dart command-line applications.
When to use this skill
- When asked to profile, optimize, or benchmark CPU execution of a Dart script
or CLI tool.
- When investigating hot loops, heavy function calls, or unexpected execution
overhead.
Workflow
- Ensure clean compilation: Make sure the target Dart script runs cleanly
(
dart run <script.dart>).
- Run Profiler Script: Use the automated profiling helper script inside
this skill directory to launch the target app with VM Service observability
enabled, capture CPU samples, and output top-consuming functions.
- Analyze & Optimize: Review the self and total sample percentages
reported by the tool to pinpoint bottlenecks (e.g., excessive object
allocation, costly hashing, virtual dispatch overhead).
Running the Profiler Helper Script
This repository includes a zero-dependency (using only official vm_service)
profiling script that launches any Dart file, connects to the VM Service, waits
for execution to complete (--pause-isolates-on-exit), retrieves CPU samples,
and prints a clean summary while exporting the full JSON profile.
Run it from any working directory:
dart run <dash_skills_repo>/skills/profile-dart-code/scripts/bin/profile.dart --out=cpu_profile.json -- <path_to_target.dart> [target_arguments...]
Script Arguments
-o, --out=<file>: Output file path to save the raw JSON CPU profile
(default: cpu_profile.json).-p, --period=<micros>: Sampling interval in microseconds (default: 1000µs
= 1ms). Minimum 50µs.-- <target.dart> [args...]: The Dart script to profile, followed by any
arguments passed to main().
[!WARNING]
Potential Hangs: When profiling or debugging Dart targets using VM services,
target exceptions or connection issues can cause the process to hang
indefinitely. Ensure your target script handles timeouts, and monitor the
process output.
Example Output
Connecting to VM service at ws://127.0.0.1:8181/ws...
Target execution paused at exit. Retrieving CPU profile samples...
=== Top CPU Functions (Self Samples) ===
1. _PuzzleSmart._shiftSlice (self: 34.2%, total: 41.0%)
2. _countInversions (self: 18.5%, total: 18.5%)
3. shortestPaths (self: 12.1%, total: 98.4%)
Saved complete JSON profile to: cpu_profile.json
Best Practices for Interpreting Profiles
- Focus on Self % vs. Total %: High
self % indicates where CPU time is
spent directly inside a function's own body (math, loop branching, array
indexing). High total % with low self % indicates a dispatcher or outer
orchestration loop.
- Look for Hidden Overhead: Watch out for implicit object allocations
(
_copyData, iterator wrappers, closure creation) inside tight loops.
- Verify Optimizations Empirically: Always record baseline sample counts
and execution duration (
time -v) before and after applying optimizations.
