MCPInstall

swift-charts

by dpearson2699Mobile

Implement, review, or improve data visualizations using Swift Charts. Use when building bar, line, area, point, pie, donut, or iOS 26 3D charts; when adding chart selection, scrolling, annotations, axes, scales, legends, or foregroundStyle grouping; when plotting functions with BarPlot, LinePlot, AreaPlot, PointPlot, Chart3D, or SurfacePlot; or when creating heat maps, Gantt charts, grouped bars, sparklines, threshold lines, or spatial visualizations.

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Pass

Install

Works with every agent the skills CLI supports.

npx skills add https://github.com/dpearson2699/swift-ios-skills --skill swift-charts
  1. 01

    Install

    Run the command in your project. The CLI asks which agents to install for.

  2. 02

    Describe the task

    Ask your agent for something this skill covers. It loads swift-charts automatically when relevant.

  3. 03

    Review the result

    The agent follows the SKILL.md steps, scripts and references bundled with the skill.

Security audits

Independent scans of the skill's instructions and bundled files.

Gen Agent Trust Hub PassSAFE ·The skill provides comprehensive guidance and code patterns for building data visualizations with Swift Charts on iOS. It covers various chart types, accessibility, performance, and interaction models without any detected security risks.
Socket PassNo alerts
Snyk PassLOW ·Risk: LOW · No issues
Runlayer PassNONE ·2 files scanned · No issues
ZeroLeaks PassNONE ·Score: 93/100 · 2 sections analyzed

SKILL.md

The instructions your agent reads when the skill is triggered.

Swift Charts

Build data visualizations with Swift Charts targeting iOS 26+. Compose marks inside Chart or Chart3D, configure axes and scales with view modifiers, and use vectorized plots or 3D plots when the data calls for them.

See references/charts-patterns.md for extended patterns, 3D charts, accessibility, and theming guidance.

Contents

Workflow

1. Build a new chart

  1. Define data as an Identifiable struct or use id: key path.
  2. Choose mark type(s): BarMark, LineMark, PointMark, AreaMark, RuleMark, RectangleMark, SectorMark, or SurfacePlot.
  3. Wrap 2D marks in Chart; use Chart3D only for real spatial or surface data.
  4. Encode visual channels: .foregroundStyle(by:), .symbol(by:), .lineStyle(by:).
  5. Configure axes with .chartXAxis / .chartYAxis.
  6. Set scale domains with .chartXScale(domain:) / .chartYScale(domain:).
  7. Add selection, scrolling, or annotations as needed.
  8. For 1000+ 2D data points, use vectorized plots (BarPlot, LinePlot, etc.).
  9. Render representative empty, typical, dense, large-text, high-contrast, and VoiceOver states; exercise selection and scrolling when present.
  10. If an encoding, axis, selection, or accessibility check fails, restore the data fixture, fix one layer, and rerun the same matrix before adding decoration.

2. Review existing chart code

Identify the data semantics before judging mark choice. Then trace every value through mark, scale, axis, style, selection, and accessibility output; run the same validation matrix used for new charts.

Chart Container

Chart(sales) { item in
    BarMark(x: .value("Month", item.month), y: .value("Revenue", item.revenue))
}

Use the data-driven initializer for a single collection. Use the content closure for mixed marks or multiple series, and pass id: when elements are not Identifiable. Load references/charts-patterns.md for complete mixed-series, theming, accessibility, and 3D recipes.

Mark Types

BarMark (iOS 16+)

// Vertical bar
BarMark(x: .value("Month", item.month), y: .value("Sales", item.sales))

// Stacked by category (automatic when same x maps to multiple bars)
BarMark(x: .value("Month", item.month), y: .value("Sales", item.sales))
    .foregroundStyle(by: .value("Product", item.product))

// Horizontal bar
BarMark(x: .value("Sales", item.sales), y: .value("Month", item.month))

// Interval bar (Gantt chart)
BarMark(
    xStart: .value("Start", item.start),
    xEnd: .value("End", item.end),
    y: .value("Task", item.task)
)

LineMark (iOS 16+)

// Single line
LineMark(x: .value("Date", item.date), y: .value("Price", item.price))

// Multi-series via foregroundStyle encoding
LineMark(x: .value("Date", item.date), y: .value("Temp", item.temp))
    .foregroundStyle(by: .value("City", item.city))
    .interpolationMethod(.catmullRom)

// Multi-series with explicit series parameter
LineMark(
    x: .value("Date", item.date),
    y: .value("Price", item.price),
    series: .value("Ticker", item.ticker)
)

PointMark (iOS 16+)

PointMark(x: .value("Height", item.height), y: .value("Weight", item.weight))
    .foregroundStyle(by: .value("Species", item.species))
    .symbol(by: .value("Species", item.species))
    .symbolSize(100)

AreaMark (iOS 16+)

// Stacked area
AreaMark(x: .value("Date", item.date), y: .value("Sales", item.sales))
    .foregroundStyle(by: .value("Category", item.category))

// Range band
AreaMark(
    x: .value("Date", item.date),
    yStart: .value("Min", item.min),
    yEnd: .value("Max", item.max)
)
.opacity(0.3)

RuleMark (iOS 16+)

RuleMark(y: .value("Target", 9000))
    .foregroundStyle(.red)
    .lineStyle(StrokeStyle(dash: [5, 3]))
    .annotation(position: .top, alignment: .leading) {
        Text("Target").font(.caption).foregroundStyle(.red)
    }

RectangleMark (iOS 16+)

RectangleMark(x: .value("Hour", item.hour), y: .value("Day", item.day))
    .foregroundStyle(by: .value("Intensity", item.intensity))

SectorMark (iOS 17+)

Use SectorMark for strictly positive values; filter, aggregate, or explain zero/negative values outside the pie or donut.

// Pie chart
Chart(data, id: \.name) { item in
    SectorMark(angle: .value("Sales", item.sales))
        .foregroundStyle(by: .value("Category", item.name))
}

// Donut chart
Chart(data, id: \.name) { item in
    SectorMark(
        angle: .value("Sales", item.sales),
        innerRadius: .ratio(0.618),
        outerRadius: .inset(10),
        angularInset: 1
    )
    .cornerRadius(4)
    .foregroundStyle(by: .value("Category", item.name))
}

Axis Customization

// Hide axes
.chartXAxis(.hidden)
.chartYAxis(.hidden)

// Custom axis content
.chartXAxis {
    AxisMarks(values: .stride(by: .month)) { value in
        AxisGridLine()
        AxisTick()
        AxisValueLabel(format: .dateTime.month(.abbreviated))
    }
}

// Multiple AxisMarks compositions (different intervals for grid vs. labels)
.chartXAxis {
    AxisMarks(values: .stride(by: .day)) { _ in AxisGridLine() }
    AxisMarks(values: .stride(by: .week)) { _ in
        AxisTick()
        AxisValueLabel(format: .dateTime.week())
    }
}

// Axis labels (titles)
.chartXAxisLabel("Time", position: .bottom, alignment: .center)
.chartYAxisLabel("Revenue ($)", position: .leading, alignment: .center)

Scale Configuration

.chartYScale(domain: 0...100)                          // Explicit numeric domain
.chartYScale(domain: .automatic(includesZero: true))   // Include zero
.chartYScale(domain: 1...10000, type: .log)            // Logarithmic scale
.chartXScale(domain: ["Mon", "Tue", "Wed", "Thu"])     // Categorical ordering

Foreground Style and Encoding

BarMark(...).foregroundStyle(.blue)                                    // Static color
BarMark(...).foregroundStyle(by: .value("Category", item.category))   // Data encoding
AreaMark(...).foregroundStyle(                                         // Gradient
    .linearGradient(colors: [.blue, .cyan], startPoint: .bottom, endPoint: .top)
)

Selection (iOS 17+)

@State private var selectedDate: Date?
@State private var selectedRange: ClosedRange<Date>?
@State private var selectedAngle: Double?

// Point selection
Chart(data) { item in
    LineMark(x: .value("Date", item.date), y: .value("Value", item.value))
}
.chartXSelection(value: $selectedDate)

// Range selection
.chartXSelection(range: $selectedRange)

// Angular selection binds the plottable angle value; derive the category from ranges.
.chartAngleSelection(value: $selectedAngle)

Scrollable Charts (iOS 17+)

Chart(dailyData) { item in
    BarMark(x: .value("Date", item.date, unit: .day), y: .value("Steps", item.steps))
}
.chartScrollableAxes(.horizontal)
.chartXVisibleDomain(length: 3600 * 24 * 7) // 7 days visible
.chartScrollPosition(initialX: latestDate)
.chartScrollTargetBehavior(
    .valueAligned(matching: DateComponents(hour: 0), majorAlignment: .page)
)

Annotations

BarMark(x: .value("Month", item.month), y: .value("Sales", item.sales))
    .annotation(position: .top, alignment: .center, spacing: 4) {
        Text("\(item.sales, format: .number)").font(.caption2)
    }

// Overflow resolution
.annotation(
    position: .top,
    overflowResolution: .init(x: .fit(to: .chart), y: .padScale)
) { Text("Label") }

Legend

.chartLegend(.hidden)                                           // Hide
.chartLegend(position: .bottom, alignment: .center, spacing: 10) // Position
.chartLegend(position: .bottom) {                                // Custom
    HStack {
        ForEach(categories, id: \.self) { cat in
            Label(cat, systemImage: "circle.fill").font(.caption)
        }
    }
}

Vectorized Plots (iOS 18+)

Use for large datasets (1000+ points). Accept entire collections or functions.

// Data-driven
Chart {
    BarPlot(sales, x: .value("Month", \.month), y: .value("Revenue", \.revenue))
        .foregroundStyle(\.barColor)
}

// Function plotting: y = f(x)
Chart {
    LinePlot(x: "x", y: "y", domain: -5...5) { x in sin(x) }
}

// Parametric: (x, y) = f(t)
Chart {
    LinePlot(x: "x", y: "y", t: "t", domain: 0...(2 * .pi)) { t in
        (x: cos(t), y: sin(t))
    }
}

Apply KeyPath-based modifiers before simple-value modifiers:

BarPlot(data, x: .value("X", \.x), y: .value("Y", \.y))
    .foregroundStyle(\.color)    // KeyPath first
    .opacity(0.8)                // Value modifier second

3D Charts (iOS 26+)

Use Chart3D for spatial data or bivariate surfaces, not as a decorative replacement for ordinary 2D categorical or time-series charts. Chart3D accepts SurfacePlot plus 3D initializers of PointMark, RuleMark, and RectangleMark.

@State private var pose: Chart3DPose = .default

Chart3D {
    SurfacePlot(x: "x", y: "y", z: "z") { x, z in
        sin(2 * x) * cos(2 * z)
    }
    .foregroundStyle(.heightBased)
}
.chartXScale(domain: -2...2)
.chartYScale(domain: -1...1)
.chartZScale(domain: -2...2)
.chart3DPose($pose)

Common Mistakes

1. Missing series parameter for multi-line charts

// WRONG -- all points connect into one line
Chart {
    ForEach(allCities) { item in
        LineMark(x: .value("Date", item.date), y: .value("Temp", item.temp))
    }
}

// CORRECT -- separate lines per city
Chart {
    ForEach(allCities) { item in
        LineMark(x: .value("Date", item.date), y: .value("Temp", item.temp))
            .foregroundStyle(by: .value("City", item.city))
    }
}

2. Too many SectorMark slices

// WRONG -- 20 tiny sectors are unreadable
Chart(twentyCategories, id: \.name) { item in
    SectorMark(angle: .value("Value", item.value))
}

// CORRECT -- group into top 5 + "Other"
Chart(groupedData, id: \.name) { item in
    SectorMark(angle: .value("Value", item.value))
        .foregroundStyle(by: .value("Category", item.name))
}

3. Missing scale domain when zero-baseline matters

// WRONG -- axis starts at ~95; small changes look dramatic
Chart(data) {
    LineMark(x: .value("Day", $0.day), y: .value("Score", $0.score))
}

// CORRECT -- explicit domain for honest representation
Chart(data) {
    LineMark(x: .value("Day", $0.day), y: .value("Score", $0.score))
}
.chartYScale(domain: 0...100)

4. Static foregroundStyle overriding data encoding

// WRONG -- static color overrides by-value encoding
BarMark(x: .value("X", item.x), y: .value("Y", item.y))
    .foregroundStyle(by: .value("Category", item.category))
    .foregroundStyle(.blue)

// CORRECT -- use only the data encoding
BarMark(x: .value("X", item.x), y: .value("Y", item.y))
    .foregroundStyle(by: .value("Category", item.category))

5. Individual marks for 10,000+ data points

// WRONG -- creates 10,000 mark views; slow
Chart(largeDataset) { item in
    PointMark(x: .value("X", item.x), y: .value("Y", item.y))
}

// CORRECT -- vectorized plot (iOS 18+)
Chart {
    PointPlot(largeDataset, x: .value("X", \.x), y: .value("Y", \.y))
}

6. Fixed chart height breaking Dynamic Type

// WRONG -- clips axis labels at large text sizes
Chart(data) { ... }
    .frame(height: 200)

// CORRECT -- adaptive sizing
Chart(data) { ... }
    .frame(minHeight: 200, maxHeight: 400)

7. KeyPath modifier after value modifier on vectorized plots

// WRONG -- compiler error
BarPlot(data, x: .value("X", \.x), y: .value("Y", \.y))
    .opacity(0.8)
    .foregroundStyle(\.color)

// CORRECT -- KeyPath modifiers first
BarPlot(data, x: .value("X", \.x), y: .value("Y", \.y))
    .foregroundStyle(\.color)
    .opacity(0.8)

8. Missing accessibility labels

// WRONG -- VoiceOver users get no context
Chart(data) {
    BarMark(x: .value("Month", $0.month), y: .value("Sales", $0.sales))
}

// CORRECT -- add per-mark accessibility
Chart(data) { item in
    BarMark(x: .value("Month", item.month), y: .value("Sales", item.sales))
        .accessibilityLabel("\(item.month)")
        .accessibilityValue("\(item.sales) units sold")
}

9. Treating angle selection as category selection

chartAngleSelection(value:) binds the selected plottable angle value. For pie and donut charts, map that numeric value through cumulative sector ranges before comparing it to a category label.

Review Checklist

  • Data model uses Identifiable or chart uses id: key path
  • Mark type matches goal (bar=comparison, line=trend, sector=proportion)
  • Multi-series lines use series: parameter or .foregroundStyle(by:)
  • Axes configured with appropriate labels, ticks, and grid lines
  • Scale domain set explicitly when zero-baseline matters
  • Pie/donut uses positive values, 5-7 sectors, and "Other" grouping
  • Selection binding type matches axis data type (Date? for date axis)
  • Pie/donut angle selection maps numeric angle values back to categories
  • Scrollable charts set .chartXVisibleDomain(length:) for viewport
  • Vectorized plots used for datasets exceeding 1000 points
  • KeyPath modifiers applied before value modifiers on vectorized plots
  • Chart3D used only for real 3D data or surfaces, with z scale and pose reviewed
  • Accessibility labels added to marks for VoiceOver
  • Chart tested with Dynamic Type and Dark Mode
  • Legend visible and positioned, or intentionally hidden
  • Ensure chart data model types are Sendable; update chart data on @MainActor

References

FAQ

What does the swift-charts skill do?

Implement, review, or improve data visualizations using Swift Charts. Use when building bar, line, area, point, pie, donut, or iOS 26 3D charts; when adding chart selection, scrolling, annotations, axes, scales, legends, or foregroundStyle grouping; when plotting functions with BarPlot, LinePlot, AreaPlot, PointPlot, Chart3D, or SurfacePlot; or when creating heat maps, Gantt charts, grouped bars, sparklines, threshold lines, or spatial visualizations.

How do I install swift-charts?

Run npx skills add https://github.com/dpearson2699/swift-ios-skills --skill swift-charts in your project. The skills CLI detects the agents you use and copies the skill into the right folder. For Claude Code you can also place the skill folder at ~/.claude/skills/swift-charts/ (personal) or .claude/skills/swift-charts/ (project).

Which AI agents can use swift-charts?

Any agent that supports the open Agent Skills format (a folder with a SKILL.md file), including Claude Code, Codex, Cursor, GitHub Copilot, Gemini CLI, Windsurf, Cline, OpenCode and more.

Is swift-charts safe to install?

Security partners have reviewed it: Gen Agent Trust Hub passed; Socket passed; Snyk passed; Runlayer passed; ZeroLeaks passed. As with any skill, read the SKILL.md and bundled scripts before installing.

Who maintains swift-charts?

It is published by dpearson2699 in dpearson2699/swift-ios-skills. It has 3,995 recorded installs.

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