ASCIIFlow
asciiflow.com
Draws boxes and arrows as plain ASCII you can paste into a comment
No sign-upOn device
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Flowcharts, wireframes, mind maps and shared canvases.
asciiflow.com
Draws boxes and arrows as plain ASCII you can paste into a comment
coggle.it
Mind maps that stay readable as branches multiply
diagrams.net
Full diagram editor that works without an account or a saved file
excalidraw.com
Hand-drawn-looking whiteboard that opens instantly with no sign-up
lucidchart.com
Polished diagramming with real-time collaboration and smart layout
markmap.js.org
Turns a Markdown outline into a collapsible mind map as you type
mermaid.live
Write a diagram as text and watch it render beside you
plantuml.com
Renders UML from a text description, with the source encoded in the URL
sequencediagram.org
Purpose-built editor for sequence diagrams, typed rather than dragged
tldraw.com
Infinite canvas that feels like a native app in a browser tab
whimsical.com
Flowcharts, wireframes, mind maps and docs on one fast canvas
wireframe.cc
Draw a rectangle and it guesses which UI element you meant
Privacy
These process everything inside the browser. Load the page, disconnect from the network, and they still work.
asciiflow.com
Draws boxes and arrows as plain ASCII you can paste into a comment
diagrams.net
Full diagram editor that works without an account or a saved file
excalidraw.com
Hand-drawn-looking whiteboard that opens instantly with no sign-up
markmap.js.org
Turns a Markdown outline into a collapsible mind map as you type
mermaid.live
Write a diagram as text and watch it render beside you
sequencediagram.org
Purpose-built editor for sequence diagrams, typed rather than dragged
tldraw.com
Infinite canvas that feels like a native app in a browser tab
By task
Archive
Kept on record so an old bookmark still leads to an answer. Each one names the site that does the job now.
gliffy.com
Browser diagramming that worked properly, until Flash stopped existing
Questions
There is no single answer, which is why this page lists 12 of them with their limits stated. If you want to avoid signing up entirely, 9 of these work with no account at all.
7 of the 12 sites here process your file inside the browser and never upload it — they are marked "On device". The rest send your input to their server, which is fine for public material and worth thinking twice about for anything personal.
Some already have. 1 entry in this category has been retired and moved to the Archive with a working successor, so an old bookmark still leads somewhere useful.