Report Formats

Overview

Lanterna supports six output formats, each suited to different workflows. The terminal format is the default; all others are available through CLI flags or the @lanternajs/report package API.

Format	How to Use	Best For
Terminal	Default output	Quick developer feedback during local development
JSON	--output report.json	CI pipelines, scripting, baseline comparison
HTML	renderHtmlReport() API	Shareable Lighthouse-style visual report
Markdown	formatMarkdownReport() API	GitHub PR comments and documentation
Perfetto	exportPerfetto() API	Deep trace analysis at ui.perfetto.dev
SpeedScope	exportSpeedScope() API	JS CPU profiling at speedscope.app

Terminal

The default output when running lanterna measure. Renders directly in the terminal with:

• Overall performance score with a colored bar visualization (green/amber/red)
• Device information (name, platform, type)
• Per-metric breakdown with individual scores and values
• Comparison deltas when a --baseline is provided (arrows indicating improvement or regression)

The terminal format uses ANSI colors and Unicode characters for visual clarity. It degrades gracefully in environments without color support.

JSON

Structured output for programmatic consumption. Export with --output path.json or generate via the report API.

The JSON schema includes: format version, timestamp, device information, overall and per-metric scores with categories, and optional sections for navigation timeline, network requests, bridge statistics, and layout data.

JSON reports serve as the interchange format for CI workflows. Save a report as a baseline, then compare subsequent runs against it to detect regressions.

HTML

A self-contained HTML file that requires no external dependencies. Features include:

• SVG gauge displaying the overall score with color coding
• Per-metric cards with individual scores, values, and category indicators
• Device and session metadata
• Comparison section with improvement/regression deltas when baseline data is available
• Automatic dark mode via prefers-color-scheme: dark using CSS custom properties

Generate via renderHtmlReport() from @lanternajs/report. See HTML Report for details.

Markdown

GitHub Flavored Markdown output designed for posting as PR comments. Includes:

• GFM-compatible tables with metric scores
• Status indicators for each metric category
• Comparison deltas with directional arrows
• Regression detection markers for metrics that dropped below threshold

Generate via formatMarkdownReport() from @lanternajs/report.

Perfetto

Chrome DevTools-compatible trace event JSON format. Each metric type maps to a named thread for timeline visualization:

• UI Thread (TID 1): UI FPS and frame drops
• JS Thread (TID 2): JS FPS
• System (TID 3): CPU and memory
• Lifecycle (TID 4): TTI

Open the exported file at ui.perfetto.dev for interactive timeline analysis. See Perfetto and SpeedScope for details.

SpeedScope

JavaScript profiling format compatible with speedscope.app. Creates one profile per metric type, allowing you to view each metric as a flame chart or time-ordered sequence.

SpeedScope exports are particularly useful for analyzing JS thread behavior alongside Hermes CPU profiles. See Perfetto and SpeedScope for details.