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docs: enhance matplotlib backend guidance in panel skills #104

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MarcSkovMadsen merged 1 commit into from
Jan 17, 2026
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docs: enhance matplotlib backend guidance in panel skills #104

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2 changes: 1 addition & 1 deletion .github/agents/holoviz-analysis-planner.agent.md
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Original file line number Diff line number Diff line change
@@ -1,7 +1,7 @@
---
name: HoloViz Analysis Planner
description: Create a detailed implementation plan for an analysis or data visualization using the HoloViz ecosystem without modifying code
tools: ['holoviz-dev/*', 'read/readFile', 'read/problems', 'agent/runSubagent', 'web/fetch', 'web/githubRepo', 'search/codebase', 'search/usages', 'search/searchResults', 'vscode/vscodeAPI']
tools: ['holoviz/*', 'read/readFile', 'read/problems', 'agent/runSubagent', 'web/fetch', 'web/githubRepo', 'search/codebase', 'search/usages', 'search/searchResults', 'vscode/vscodeAPI']
handoffs:
- label: Implement Plan
agent: agent
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27 changes: 27 additions & 0 deletions src/holoviz_mcp/config/resources/skills/panel.md
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Expand Up @@ -537,6 +537,33 @@ def kpi_value(self):

DO follow the hvplot and holoviews best practice guides!

### Matplotlib

**CRITICAL**: On windows set non-interactive backend before importing matplotlib.pyplot:

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The guidance incorrectly suggests that setting the 'agg' backend is only necessary on Windows. The 'agg' backend should be set on all platforms when using matplotlib with Panel for server-side rendering, not just Windows. Consider revising to: "CRITICAL: Set non-interactive backend before importing matplotlib.pyplot:" or "CRITICAL: When using Panel with matplotlib, set non-interactive backend before importing matplotlib.pyplot:"

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**CRITICAL**: On windows set non-interactive backend before importing matplotlib.pyplot:
**CRITICAL**: When using Panel with matplotlib, set a non-interactive backend (e.g. `'agg'`) before importing matplotlib.pyplot:

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Copilot AI Jan 17, 2026

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The word "windows" should be capitalized to "Windows" when referring to the operating system.

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**CRITICAL**: On windows set non-interactive backend before importing matplotlib.pyplot:
**CRITICAL**: On Windows set non-interactive backend before importing matplotlib.pyplot:

Copilot uses AI. Check for mistakes.

**Why**: The `'agg'` backend is required for server-side rendering without display. Panel needs to render plots as images, not interactive GUI windows.

**Extension**: DON'T include `'matplotlib'` in `pn.extension()` - it doesn't require JavaScript loading like Plotly or Bokeh extensions.

```python
# ✅ CORRECT
import matplotlib
matplotlib.use('agg')
import matplotlib.pyplot as plt
import panel as pn

pn.extension() # No 'matplotlib' needed

# ❌ WRONG
pn.extension('matplotlib') # Not a Panel extension
```

**Best Practices**:

- DO use matplotlib for publication-quality static plots
- DO close figures after rendering to prevent memory leaks: `plt.close(fig)`
- DO consider hvPlot or Plotly for interactive plots instead

### Plotly

Do set the template (theme) depending on the `theme` of the app.
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