This is online power-up/power down sequence diagram constructor. Its pretty basic, but get job done. There is no subscriprions, no ads. It can create black and white diagrams (checkbox on top left). I`ve no idea in web programming so all code was written by Gemini.

Link: https://lemon-zz.github.io/power_rails_sequence_gen/

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Mods by Kristian Bergh using Gemini (Mods summary also generated by Gemini)

🚀 Major Engine & Logic Updates

• Advanced Color Management Engine: Replaced the basic hardcoded color assignment with a dynamic 10-algorithm auto-coloring engine (featuring modes like Adjacency Max, Size-Weighted, Rainbow Cascade, and Randomize).
• Auto/Manual Color Modes: Added the ability to set traces to Auto (A) or Manual (M) color modes. Includes a custom color picker popup with a lightness slider, HEX override, and buttons to selectively re-roll auto traces, force children to inherit parent colors, or reset all colors.
• Intelligent Power-Down Cloning: The original cloning function blindly reversed the entire list. This has been split into two tools: "Clone PD - Flat" for a standard reverse, and "Clone PD - Groups", which smartly identifies root enablers versus leaf nodes, reversing the backbone sequence while maintaining accurate topological parent-child groupings. Time break definitions are now perfectly preserved during the cloning process.
• Logical Time Breaks: Time breaks are no longer placed by their physical array order. They now use exact logical positioning via a startTime parameter, allowing the math engine to dynamically compress the surrounding timeline.

🖥️ UI & Workflow Enhancements

• Zoom & Auto-Fit: Introduced a dynamic canvas scaling system with a manual Zoom percentage input and an "Auto Fit" toggle to automatically fit the sequence to your screen width.
• Advanced Rail Triggers: Individual rails now support partial parent triggering (triggerPct) and additional delays (addDelay), expanding upon the original base delay and rise time constraints.
• Sequence Reordering: Added "Move to Top" (⇈) and "Move to Bottom" (⇊) buttons on item cards to drastically speed up list organization.
• Break Muting: Added a toggleable mute button (👁️/🙈) for Time Breaks, allowing users to temporarily bypass a break in the rendering engine without having to delete and recreate it.
• Configuration Saving/Loading: Added fully supported JSON state saving and loading, ensuring all rail configurations, timing, colors, and layout settings are perfectly stored and recalled.
• Authorship: The meta tags have been updated to reflect joint authorship between Lemon_ZZ and Kristian Bergh.

🎨 Rendering & Visual Polish

• Decoupled Rendering Math: The drawing engine now strictly separates logical time from physical X-coordinates, allowing for completely accurate time-scaling and dynamic break compression.
• Measurement Arrows: The yellow timing measurement arrows were moved cleanly above the signal traces. They now automatically calculate and display the final summed time (Delay + Add. Delay + Rise) rather than cluttered individual terms.
• Tick-Mark Formatting: Added half-height, downward-facing tick marks on the measurement arrows to delineate delay vs. rise time phases, which intelligently hide themselves if the visual space is too tight.
• Z-Index Layering: Rewrote the SVG drawing order to fix visual clumping. The background time grid and total time indicators now cleanly route underneath Time Break graphics, while marker text and measurement arrows float safely on top.