panel

Panel

Panel is a Python library for building interactive dashboards, data apps, and tools entirely in Python — no JavaScript required. It connects widgets to plots, tables, and text with reactive callbacks, and serves the result as a web application.

Always use a pn.viewable.Viewer class to structure apps. This keeps state, layout, and logic organized and avoids flickering from recreated components. Once an app outgrows one class — multiple views over shared data, state several components touch — split it into composable classes (see Designing Panel Architecture).

Contents

• Lookup — component docs URLs and site search
• References — iterative development, Material UI, plotting, data storytelling, custom components, React shells, Playwright testing, app structure & scaling, review
• Viewer Class Pattern
• Widgets and Extensions
• Defaults
• Templates and Layouts
• Serving Workflow
• Performance

Lookup

Fetch Panel docs as markdown, not HTML: prefix any Panel doc path with /markdown/ and change .html/.ipynb to .md (also for links found inside pages), e.g https://panel.holoviz.org/markdown/tutorials/basic/build_dashboard.md. If the result is empty, the page moved — use the llms.txt index: https://panel.holoviz.org/llms.txt.

• Anything else: web-search https://panel.holoviz.org/search.html?q=<topic>, then convert the .html hit to its /markdown/…​.md URL.

References

Read these for specialized topics. Each is a standalone document you can load on demand.

• Iterating on Panel Apps — pre-flight lint, serve with logging, panel-live-server MCP tools, live-browser layout lint, Bokeh plot-model inspection, startup benchmarking, screenshot with Playwright, review and debug agentic loop
• Designing Panel Architecture — composing larger apps (State/DataStore/View/App, param.ClassSelector, cross-object @param.depends, from_data, pn.rx) and runtime/scale (per-session model, pn.state scheduling, URL state sync, generator streaming, caching tiers, nthreads, profiling)
• Building Custom Components — Python-vs-JS decision ladder; pure-Python Viewer/PyComponent; JSComponent, ReactComponent, AnyWidgetComponent, MaterialUIComponent; CDN selection, event handling, state sync lifecycle
• Wrapping React Apps — making an existing React/JSX UI the whole app: shell/app class split, model.useState as the only transport, Child embedding of Panel components, request/response param pairs, shadow-DOM CSS rules, _importmap externals, panel compile and the dev-vs-production bundle trap
• Using Material UI — building pmui apps: pmui.Page, Container/Grid layouts, centering, component gotchas
• Theming Material UI — theme_config palette, typography, web fonts, component overrides, icons, brand assets, chart colors and plot fonts
• Migrating to Material UI — converting an existing plain-Panel app to pmui: template→Page, widget swaps, pane/interaction upgrades, what to leave alone
• Converting Designs to Material UI — workflow for turning a screenshot/design/React app into a pmui app: capture references, map to components, build component-first with mock data, assemble, theme last
• Plotting in Panel — embedding plots from any library: HoloViews/hvPlot (DynamicMap zoom/pan, responsive sizing), Matplotlib, Plotly, ECharts, Bokeh toolbar tools
• Data Storytelling — assembling explanatory charts into a scrollable editorial article (pmui masthead, narrow reading column, prose-then-chart rhythm, one visual family); see examples/graphic_story.py
• Using Tabulator — add_filter with widgets, checkbox selection, row content, function-based filtering
• Using Pytest Playwright — serve_component/wait_until utilities, JS↔Python sync tests, complete test patterns for custom components
• Reviewing Panel Apps — anti-pattern checklist for code review: flickering, missing hold, watcher gaps, reactive-wiring priority, from_param super() ordering, mutation bugs
• Troubleshooting Panel Apps — symptom→cause→fix for apps that serve but misbehave silently: init ordering, dead-app, blank Page, responsive/spinner issues, version & deprecation diagnosis