Polypane vs Sizzy vs Responsively: An Honest Comparison
A straight comparison of the three main multi-device development browsers - strengths, weaknesses, and which one fits your workflow.
8 min read - Updated 2026-06-12
Use this guide as a compact release reference, then validate the same breakpoints in Sizzy with synchronized devices and screenshot evidence.
The short version
All three show your site on multiple viewports at once, and all three are good at it. Responsively is free and open source - the right starting point if budget is the constraint. Polypane (from ~$10/mo) leans into accessibility audits, contrast checking, and social preview tooling. Sizzy ($12-15/mo or $499 lifetime) focuses on fast multi-device workflows: synced interactions, isolated sessions, project workspaces, and screenshot tooling. This is Sizzy's blog, so take our framing with that grain of salt - but the feature breakdown below is accurate.
Responsively: free, open source, community-maintained
Polypane: strongest accessibility and meta-preview tooling
Sizzy: strongest session/workspace workflow and screenshot tooling
All three: Chromium-based with side-by-side viewports
Where each one wins
Responsively covers the core need - side-by-side previews with mirrored scrolling - at zero cost, though maintenance is volunteer-driven and simulation depth is thinner. Polypane is excellent if accessibility compliance is a daily requirement: live WCAG contrast checks, screen reader previews, and 20+ debug overlays. Sizzy is built for shipping responsive products fast: multiple isolated sessions for testing different auth states simultaneously, per-project workspaces, Photo Studio for framed marketing screenshots, and full-time maintenance since 2018.
Choose Responsively if free is the requirement
Choose Polypane if accessibility auditing drives your day
Choose Sizzy for multi-session testing and project workflows
Avoid all three if you rarely do responsive work - DevTools is fine
The honest way to decide
Both paid options have free trials (Sizzy's is 14 days with no credit card; Polypane offers a trial as well) and Responsively costs nothing to try. Install the candidates, open your real project, and run your actual workflow for a day in each. The right tool becomes obvious within hours - it's the one you stop noticing.
Test with your real project, not a demo site
Run your most annoying recent bug through each tool
Check the features you'd use weekly, not the longest feature list
Factor in maintenance pace and support responsiveness
Release checklist
List your top three responsive-workflow pain points.
Trial each candidate against a real project for one day.
Compare only the features you would use weekly.
Pick the tool that disappears into your workflow.
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