data-visualization
Create effective data visualizations with Python (matplotlib, seaborn, plotly). Use when building charts, choosing the right chart type for a dataset, creating publication-quality figures, or applying design principles like accessibility and color theory.
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Install
Works with every agent the skills CLI supports.
npx skills add https://smithery.ai --skill data-visualization- 01
Install
Run the command in your project. The CLI asks which agents to install for.
- 02
Describe the task
Ask your agent for something this skill covers. It loads data-visualization automatically when relevant.
- 03
Review the result
The agent follows the SKILL.md steps, scripts and references bundled with the skill.
SKILL.md
The instructions your agent reads when the skill is triggered.
Data Visualization Skill
Chart selection guidance, Python visualization code patterns, design principles, and accessibility considerations for creating effective data visualizations.
Chart Selection Guide
Choose by Data Relationship
| What You're Showing | Best Chart | Alternatives |
|---|---|---|
| Trend over time | Line chart | Area chart (if showing cumulative or composition) |
| Comparison across categories | Vertical bar chart | Horizontal bar (many categories), lollipop chart |
| Ranking | Horizontal bar chart | Dot plot, slope chart (comparing two periods) |
| Part-to-whole composition | Stacked bar chart | Treemap (hierarchical), waffle chart |
| Composition over time | Stacked area chart | 100% stacked bar (for proportion focus) |
| Distribution | Histogram | Box plot (comparing groups), violin plot, strip plot |
| Correlation (2 variables) | Scatter plot | Bubble chart (add 3rd variable as size) |
| Correlation (many variables) | Heatmap (correlation matrix) | Pair plot |
| Geographic patterns | Choropleth map | Bubble map, hex map |
| Flow / process | Sankey diagram | Funnel chart (sequential stages) |
| Relationship network | Network graph | Chord diagram |
| Performance vs. target | Bullet chart | Gauge (single KPI only) |
| Multiple KPIs at once | Small multiples | Dashboard with separate charts |
When NOT to Use Certain Charts
- Pie charts: Avoid unless <6 categories and exact proportions matter less than rough comparison. Humans are bad at comparing angles. Use bar charts instead.
- 3D charts: Never. They distort perception and add no information.
- Dual-axis charts: Use cautiously. They can mislead by implying correlation. Clearly label both axes if used.
- Stacked bar (many categories): Hard to compare middle segments. Use small multiples or grouped bars instead.
- Donut charts: Slightly better than pie charts but same fundamental issues. Use for single KPI display at most.
Python Visualization Code Patterns
Setup and Style
import matplotlib.pyplot as plt
import matplotlib.ticker as mticker
import seaborn as sns
import pandas as pd
import numpy as np
# Professional style setup
plt.style.use('seaborn-v0_8-whitegrid')
plt.rcParams.update({
'figure.figsize': (10, 6),
'figure.dpi': 150,
'font.size': 11,
'axes.titlesize': 14,
'axes.titleweight': 'bold',
'axes.labelsize': 11,
'xtick.labelsize': 10,
'ytick.labelsize': 10,
'legend.fontsize': 10,
'figure.titlesize': 16,
})
# Colorblind-friendly palettes
PALETTE_CATEGORICAL = ['#4C72B0', '#DD8452', '#55A868', '#C44E52', '#8172B3', '#937860']
PALETTE_SEQUENTIAL = 'YlOrRd'
PALETTE_DIVERGING = 'RdBu_r'
Line Chart (Time Series)
fig, ax = plt.subplots(figsize=(10, 6))
for label, group in df.groupby('category'):
ax.plot(group['date'], group['value'], label=label, linewidth=2)
ax.set_title('Metric Trend by Category', fontweight='bold')
ax.set_xlabel('Date')
ax.set_ylabel('Value')
ax.legend(loc='upper left', frameon=True)
ax.spines['top'].set_visible(False)
ax.spines['right'].set_visible(False)
# Format dates on x-axis
fig.autofmt_xdate()
plt.tight_layout()
plt.savefig('trend_chart.png', dpi=150, bbox_inches='tight')
Bar Chart (Comparison)
fig, ax = plt.subplots(figsize=(10, 6))
# Sort by value for easy reading
df_sorted = df.sort_values('metric', ascending=True)
bars = ax.barh(df_sorted['category'], df_sorted['metric'], color=PALETTE_CATEGORICAL[0])
# Add value labels
for bar in bars:
width = bar.get_width()
ax.text(width + 0.5, bar.get_y() + bar.get_height()/2,
f'{width:,.0f}', ha='left', va='center', fontsize=10)
ax.set_title('Metric by Category (Ranked)', fontweight='bold')
ax.set_xlabel('Metric Value')
ax.spines['top'].set_visible(False)
ax.spines['right'].set_visible(False)
plt.tight_layout()
plt.savefig('bar_chart.png', dpi=150, bbox_inches='tight')
Histogram (Distribution)
fig, ax = plt.subplots(figsize=(10, 6))
ax.hist(df['value'], bins=30, color=PALETTE_CATEGORICAL[0], edgecolor='white', alpha=0.8)
# Add mean and median lines
mean_val = df['value'].mean()
median_val = df['value'].median()
ax.axvline(mean_val, color='red', linestyle='--', linewidth=1.5, label=f'Mean: {mean_val:,.1f}')
ax.axvline(median_val, color='green', linestyle='--', linewidth=1.5, label=f'Median: {median_val:,.1f}')
ax.set_title('Distribution of Values', fontweight='bold')
ax.set_xlabel('Value')
ax.set_ylabel('Frequency')
ax.legend()
ax.spines['top'].set_visible(False)
ax.spines['right'].set_visible(False)
plt.tight_layout()
plt.savefig('histogram.png', dpi=150, bbox_inches='tight')
Heatmap
fig, ax = plt.subplots(figsize=(10, 8))
# Pivot data for heatmap format
pivot = df.pivot_table(index='row_dim', columns='col_dim', values='metric', aggfunc='sum')
sns.heatmap(pivot, annot=True, fmt=',.0f', cmap='YlOrRd',
linewidths=0.5, ax=ax, cbar_kws={'label': 'Metric Value'})
ax.set_title('Metric by Row Dimension and Column Dimension', fontweight='bold')
ax.set_xlabel('Column Dimension')
ax.set_ylabel('Row Dimension')
plt.tight_layout()
plt.savefig('heatmap.png', dpi=150, bbox_inches='tight')
Small Multiples
categories = df['category'].unique()
n_cats = len(categories)
n_cols = min(3, n_cats)
n_rows = (n_cats + n_cols - 1) // n_cols
fig, axes = plt.subplots(n_rows, n_cols, figsize=(5*n_cols, 4*n_rows), sharex=True, sharey=True)
axes = axes.flatten() if n_cats > 1 else [axes]
for i, cat in enumerate(categories):
ax = axes[i]
subset = df[df['category'] == cat]
ax.plot(subset['date'], subset['value'], color=PALETTE_CATEGORICAL[i % len(PALETTE_CATEGORICAL)])
ax.set_title(cat, fontsize=12)
ax.spines['top'].set_visible(False)
ax.spines['right'].set_visible(False)
# Hide empty subplots
for j in range(i+1, len(axes)):
axes[j].set_visible(False)
fig.suptitle('Trends by Category', fontsize=14, fontweight='bold', y=1.02)
plt.tight_layout()
plt.savefig('small_multiples.png', dpi=150, bbox_inches='tight')
Number Formatting Helpers
def format_number(val, format_type='number'):
"""Format numbers for chart labels."""
if format_type == 'currency':
if abs(val) >= 1e9:
return f'${val/1e9:.1f}B'
elif abs(val) >= 1e6:
return f'${val/1e6:.1f}M'
elif abs(val) >= 1e3:
return f'${val/1e3:.1f}K'
else:
return f'${val:,.0f}'
elif format_type == 'percent':
return f'{val:.1f}%'
elif format_type == 'number':
if abs(val) >= 1e9:
return f'{val/1e9:.1f}B'
elif abs(val) >= 1e6:
return f'{val/1e6:.1f}M'
elif abs(val) >= 1e3:
return f'{val/1e3:.1f}K'
else:
return f'{val:,.0f}'
return str(val)
# Usage with axis formatter
ax.yaxis.set_major_formatter(mticker.FuncFormatter(lambda x, p: format_number(x, 'currency')))
Interactive Charts with Plotly
import plotly.express as px
import plotly.graph_objects as go
# Simple interactive line chart
fig = px.line(df, x='date', y='value', color='category',
title='Interactive Metric Trend',
labels={'value': 'Metric Value', 'date': 'Date'})
fig.update_layout(hovermode='x unified')
fig.write_html('interactive_chart.html')
fig.show()
# Interactive scatter with hover data
fig = px.scatter(df, x='metric_a', y='metric_b', color='category',
size='size_metric', hover_data=['name', 'detail_field'],
title='Correlation Analysis')
fig.show()
Design Principles
Color
- Use color purposefully: Color should encode data, not decorate
- Highlight the story: Use a bright accent color for the key insight; grey everything else
- Sequential data: Use a single-hue gradient (light to dark) for ordered values
- Diverging data: Use a two-hue gradient with neutral midpoint for data with a meaningful center
- Categorical data: Use distinct hues, maximum 6-8 before it gets confusing
- Avoid red/green only: 8% of men are red-green colorblind. Use blue/orange as primary pair
Typography
- Title states the insight: "Revenue grew 23% YoY" beats "Revenue by Month"
- Subtitle adds context: Date range, filters applied, data source
- Axis labels are readable: Never rotated 90 degrees if avoidable. Shorten or wrap instead
- Data labels add precision: Use on key points, not every single bar
- Annotation highlights: Call out specific points with text annotations
Layout
- Reduce chart junk: Remove gridlines, borders, backgrounds that don't carry information
- Sort meaningfully: Categories sorted by value (not alphabetically) unless there's a natural order (months, stages)
- Appropriate aspect ratio: Time series wider than tall (3:1 to 2:1); comparisons can be squarer
- White space is good: Don't cram charts together. Give each visualization room to breathe
Accuracy
- Bar charts start at zero: Always. A bar from 95 to 100 exaggerates a 5% difference
- Line charts can have non-zero baselines: When the range of variation is meaningful
- Consistent scales across panels: When comparing multiple charts, use the same axis range
- Show uncertainty: Error bars, confidence intervals, or ranges when data is uncertain
- Label your axes: Never make the reader guess what the numbers mean
Accessibility Considerations
Color Blindness
- Never rely on color alone to distinguish data series
- Add pattern fills, different line styles (solid, dashed, dotted), or direct labels
- Test with a colorblind simulator (e.g., Coblis, Sim Daltonism)
- Use the colorblind-friendly palette:
sns.color_palette("colorblind")
Screen Readers
- Include alt text describing the chart's key finding
- Provide a data table alternative alongside the visualization
- Use semantic titles and labels
General Accessibility
- Sufficient contrast between data elements and background
- Text size minimum 10pt for labels, 12pt for titles
- Avoid conveying information only through spatial position (add labels)
- Consider printing: does the chart work in black and white?
Accessibility Checklist
Before sharing a visualization:
- Chart works without color (patterns, labels, or line styles differentiate series)
- Text is readable at standard zoom level
- Title describes the insight, not just the data
- Axes are labeled with units
- Legend is clear and positioned without obscuring data
- Data source and date range are noted
FAQ
What does the data-visualization skill do?
Create effective data visualizations with Python (matplotlib, seaborn, plotly). Use when building charts, choosing the right chart type for a dataset, creating publication-quality figures, or applying design principles like accessibility and color theory.
How do I install data-visualization?
Run npx skills add https://smithery.ai --skill data-visualization 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/data-visualization/ (personal) or .claude/skills/data-visualization/ (project).
Which AI agents can use data-visualization?
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 data-visualization safe to install?
No partner security audit is available yet. Skills can run commands and scripts, so read the SKILL.md and any bundled files before installing.
Who maintains data-visualization?
It is published by smithery.ai in smithery.ai. It has 330 recorded installs.
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