Free responsive website checker for mobile, tablet and desktop
Stable domains for local development ports, eliminating conflicts with free open-source tunnels and paid cloud options
Stage
Not given
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Founded
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Based in
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Pricing model
Free
Freemium
Pricing
Not given
Free and Open Source: $0 (unlimited local tunnels, open source); Professional: $49/mo or $490/yr (unlimited cloud tunnels, visitor auth, feedback comments); Team: $149/mo or $1,490/yr (everything in Professional plus unlimited members, teams, shared subdomains, approvals, organization billing); Ente
Key features
Test multiple device viewports simultaneously
Real CSS viewport rendering
Share setup links
Custom pixel width testing
No installation required
Sync scroll across panes
Browser-based with no account needed
Stable local domains (*.portzero.local) for processes and containers
Cloud tunnels (*.tunnel.portzero.cloud) with HTTPS for LAN and internet access
Support for multiple programming languages
Git worktree support with per-branch URLs
AI agent integration with MCP server
Visitor authentication and access control
Feedback comments on live tunnels
Team access policies and approvals
Audit log (Enterprise plan)
Organization billing with no per-seat charges
What makes it different
Compare multiple real device widths side by side instead of switching one at a time
Faster than DevTools for checking several device sizes at once
Entirely browser-based with no setup, signup or download
Built and maintained by one developer in the open
Eliminates port conflicts by assigning stable virtual domains instead of port numbers
Free and open source for local use; no additional cost for cloud features on paid plans
Flat pricing with no meters, overages, or per-seat charges
Agent-ready with native MCP server integration for AI coding agents
Works across multiple OS and languages with zero port bookkeeping required
Responsive Tool
Port Zero