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Feature checklists make every tool look equivalent. This table leads with the three things that actually differ — what it costs you before it works, whether your files leave your device, and where the free version stops.
| ASCIIFlowasciiflow.com | diagrams.netdiagrams.net | Excalidrawexcalidraw.com | Mermaid Live Editormermaid.live | |
|---|---|---|---|---|
| What it does | Draws boxes and arrows as plain ASCII you can paste into a comment | Full diagram editor that works without an account or a saved file | Hand-drawn-looking whiteboard that opens instantly with no sign-up | Write a diagram as text and watch it render beside you |
| What it costs you | No sign-upWorks the moment the page loads. No account, no email, no trial. | No sign-upWorks the moment the page loads. No account, no email, no trial. | No sign-upWorks the moment the page loads. No account, no email, no trial. | No sign-upWorks the moment the page loads. No account, no email, no trial. |
| Your files | Runs on your device | Runs on your device | Runs on your device | Runs on your device |
| Where it stops | Output is monospaced characters only, and it breaks visually for anyone reading in a proportional font. | No automatic layout — a fifty-box diagram is fifty boxes you positioned yourself. | Local drawings have no version history — clearing browser storage loses them permanently. | Layout is decided by the renderer — if it routes an edge badly there is no way to drag it. |
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| Category | Diagrams & Whiteboards | Diagrams & Whiteboards | Diagrams & Whiteboards | Diagrams & Whiteboards |
| Last checked | 2026-07-29 | 2026-07-29 | 2026-07-29 | 2026-07-29 |
| Open the site | Open | Open | Open | Open |
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