Show HN: GUI for editing Mermaid class diagrams | Hacker News Reader

Show HN: GUI for editing Mermaid class diagrams

docs.mermaidchart.com

230 pointsknsv59 comments

My front end to mermaid is usually claude. I can’t count how many times trying to convey a complicated idea (last week, a one time use token in a 3 party where my backend can’t talk to the client) has been made simple to explain with a quick diagram claude made.

I am a paid mermaid account holder but claude is still my first front end, because it’s the tool I’m in most of the time anyway. What I’m excited for in the GUI is I can take that quick diagram and add the styling, colors, and hopefully move some of the boxes around such that the arrows are better than the auto layout drops them.

From reading the blog post, the first thing I’d like which is changing the visual colors and styling of individual boxes in the diagram might be missed. I find that the most time consuming thing to do manually with the code, I would love to see rich tools there.

Very interesting. Any hiccups?

I just tried this last week for the first time. I asked claude to create a syntax diagram for a toy grammar. The resulting mermaid source had a syntax error (unescaped special character). Despite having its own mermaid widget thingie, I couldn't compel claude to fix its own code.

I haven’t had issues with it enough to notice, but I do tolerate it making code mistakes as just part of the deal now. I fix the little errors (claude said it made a deps.edn file for a clojure project but it’s actually lien format) as just part of the deal. I might not have just papered over the issues in my brain

Hi all, I'm Dominic and I'm on the product team at Mermaid. I enjoyed reading a lot of your feedback!

It seems there's several good ideas and thoughts on the direction of the platform that we'd love to learn more about. If you have problems with the current product, improvement requests, or would like to chat then let's connect! Please email me at dominic@mermaidchart.com or book time on my calendar: (https://calendly.com/dominic-01w/mermaid-shapers-product-int...)

Thanks for taking a look at our latest release!

Any idea when Mermaid diagrams will render outside of web browsers?

https://github.com/mermaid-js/mermaid/issues/2485

<rant> Aside, I'm the author of KeenWrite (https://keenwrite.com/), a Markdown text editor that allows embedding diagrams using the triple-backtick syntax. Here's a GraphViz example:

    ``` diagram-graphviz
    digraph {
        rankdir="LR";
        a -> b -> c;
    }
    ```

KeenWrite parses the `diagram-` prefix then passes the word `graphviz` to Kroki (https://kroki.io/), which has an API for rendering a variety of ASCII diagrams, including Mermaid. Meaning, if Kroki adds a new diagram type, KeenWrite gets it for free (without modification).

In Markdown, formatting a source code snippet entails using the standard syntax for code blocks:

    ``` graphviz
    digraph {
        rankdir="LR"
        a -> b -> c;
    }
    ```

GitHub created a de facto standard for Mermaid diagrams that breaks the convention of having triple-backticks followed by a language identifier to show the source code for that language in a monospace font. This was an unfortunate decision. </rant>

Hello Dominic.

Seconding the question on browserless rendering in the other comment. Having to (unseccessfully for us so far; the text renders incorrectly) tweak selenium setups to do headless builds is madness and I would have thought this to be top prio as a base feature beyond PoC for anything aiming for wide adoption.

I think there are two slightly different issues here!

1. SVGs generated by Mermaid use the SVG 2 features, but other than browsers, most libraries only support SVG 1.1 features, i.e. <https://github.com/mermaid-js/mermaid/issues/2102>, which is what the other comment mentioned.

2. Mermaid requires a browser layout engine to render the diagrams (your issue), i.e. <https://github.com/mermaid-js/mermaid/issues/3650>. This is something I also really want to fix (I maintain the [`mermaid-js/mermaid-cli`][1] project and we need to use Puppeteer/Headless Chrome to render mermaid diagrams, which isn't ideal.) However, I don't think this would be easy, since we'd need a browserless tool that supports a browser-like layout engine (although I'm hoping that [Servo][2] might eventually be able to support it).

And if you do want to do headless renders of Mermaid diagrams, I'd recommend using (or adapting, since the code is all MIT licensed and I'm not aware of one that uses Selenium):

- <https://github.com/mermaid-js/mermaid-cli>, which uses Puppeteer as the headless browser API.

- <https://github.com/remcohaszing/mermaid-isomorphic>, which uses Playwright as the headless browser API.

And make sure that whatever server is doing the headless renders of Mermaid diagrams has all the correct fonts installed!

[1]: https://github.com/mermaid-js/mermaid-cli

[2]: https://servo.org/

I’d like to see better controls for keeping diagram components from colliding. I’m sure that’s a nontrivial ask, but I run into poorly placed components quite frequently, and I feel like that’d be a major selling point for Mermaid for me if you could solve it

I spent some time playing around with this recently and loved it at first. I also realized ChatGPT is pretty good at generating Mermaid diagrams (didn't try your own AI features).

However after getting into it some I ran into some significant frustrations. After creating a medium-complexity diagram, I was excited to see the Whiteboard feature to drag things around / improve the layout manually. But it really started breaking, it just wouldn't let me organize/drag things where I wanted, and I couldn't get things to not overlap. I also wished more diagram types supported Whiteboard (I noticed some didn't).

Also I some confusion between the capabilities of mermaidchart.com and mermaid.live. Are these competitors? Variations of similar apps. I was confused. Also "Playground" vs "Live Editor" is confusing.

Overall glad this exists and hope it continues to improve.

I had the exact same set of issues and questions.

> it just wouldn't let me organize/drag things where I wanted, and I couldn't get things to not overlap

I suspect this might be a fundamental issue with mermaid. I've always had issues getting it to lay things out in any other way than how it "wants" me to, with giant gaps between things

This is definitely a gap in current Mermaid functionality. This is a gap we're aiming to close in 2025. Significant Whiteboard improvements and expanded diagram support is on the way! If you have a specific use case or diagram type you'd like us to keep in mind then let me know! dominic@mermaidchart.com

Thanks for your comment:)

Hi there, Mermaid CEO here:)

I hear you on the whiteboard. It's still in its early days. Should be substantially improved in the coming months.

To clarify on mermaidchart.com and mermaid.live, we are the same team. Mermaid.live is our fully open source hosted editor. This was the original editor for our 10 year old open source project. The creator of Mermaid recently founded mermaidchart.com with the CEO of Gitlab's venture studio to expand the capabilities of Mermaid for more users and build an enterprise grade product. The company is open core and venture backed. The Mermaid project will remain forever open source and will continue to invest in growing it and the company for those that desire more advanced business features.

We really appreciate your feedback and support. Ping me if you'd like to chat with our product team about the features you're hoping for:) andrew@mermaidchart.com

Please forgive my posting on the broader topic of Mermaid... The Mermaid package has gotten much bigger recently. Compare mermaid.min.js across a sampling of major releases:

     9.2.2  2022-11-09  1.09 MB 
     9.3.0  2022-12-15   899 kB
     9.4.0  2023-02-15  2.82 MB
    10.9.1  2024-05-14  3.34 MB
    11.4.1  2024-11-27  2.57 MB

All the new features are really cool, and maybe this is "fine" when mermaid itself is the purpose of the website (like this submission), but it's a bigger burden when mermaid is a value-add for generic markdown documentation: every visitor has to download and execute 3+MB of js just to view simple diagrams, or worse even when there are no diagrams on that page at all.

Is there a plan to reduce the required bundle size for viewers and users that only use a small subset of mermaid's wide feature set?

Good choice of a product name. Totally applicable. /s I know single-word, unrelated product labelling is the shit for quite some years now.

Props for somehow convincing all the foundation models to generate charts using your markup. It is guaranteed to survive a very long time now.

Mermaid CEO is probably the coolest title I've ever heard

It is pretty cool! But,

https://news.ycombinator.com/item?id=14908052

I watched the How the Universe Works series, on HBO, and they have this lady that is a Planetary Protection Engineer.

She has her own Web site: https://www.moogega.com

I only use diagramming tools with automatic layout algos to generate visualizations programmatically to debug things. For documentation purpose, I largely prefer to draw them by hand using OmniGraffle, because making graphs look nice using tools like graphviz is very complex and you find yourself abusing features to hack your vision into reality

What's dearly needed in my opinion is a graph layout algo based on a machine learning model (so that it can take into account readability and aesthetics). Unfortunately what I found so far is mostly concerned with displaying large graphs, which is kind of another domain altogether.

I hope Mermaid is collecting every single edition point that happens on their UI, that would make for a nice dataset I guess.

Also, some interesting links I stumbled upon while exploring this space:

Graphviz-like generic graph-drawing library. More options, more control.

https://eclipse.dev/elk/

Experiments by the same team responsible for the development of ELK, at Kiel University

https://github.com/kieler/KLighD

Kieler project wiki

https://rtsys.informatik.uni-kiel.de/confluence/display/KIEL...

Constraint-based graph drawing libraries

https://www.adaptagrams.org/

JS implementation

https://ialab.it.monash.edu/webcola/

Some cool stuff:

HOLA: Human-like Orthogonal Network Layout

https://ialab.it.monash.edu/~dwyer/papers/hola2015.pdf

Confluent Graphs demos: makes edges more readable.

https://www.aviz.fr/~bbach/confluentgraphs/

Stress-Minimizing Orthogonal Layout of Data Flow Diagrams with Ports

https://arxiv.org/pdf/1408.4626.pdf

Improved Optimal and Approximate Power Graph Compression for Clearer Visualisation of Dense Graphs

https://arxiv.org/pdf/1311.6996v1.pdf

I settled on excalidraw via obsidian

https://github.com/zsviczian/obsidian-excalidraw-plugin

This is really impressive! Excalidraw does some great work. Did you try Mermaid's integration with Obsidian? What was lacking and what ultimately hooked you on Excalidraw?

I do use mermaid quite a bit in markdown because it's documentation/code that can be updated, the idea tends to start in my notes as excalidraw, and eventually become a mermaid graph. I wouldn't say it's lacking anything. I have not tried it so I can't a valid opinion, but I am happy to give it a try and give some feedback. I do waste time converting. I see a couple of tools, do you recommend one in particular?

The only reason anyone uses mermaid is because it's low friction and most editors support it out of the box or through plugins.

But its layouting engine sucks and everything requires hacks and workarounds and configuration tweaks to display properly. Only the most trivial graphs render nicely on the first try.

All I really want to do is define how to actually lay out the blocks using a DSL so that they don't look like absolute shit. I hate drag and drop UIs and I hate mermaid. There's no decent code-first diagram building tool out there, let alone one that I can embed into my notes as easily as mermaid.

I think you'd like https://treevis.net

We make (and sell) one, you can play with it here: https://play.d2lang.com/?script=qlDQtVOo5AIEAAD__w%3D%3D&lay...

Bigger example: https://play.d2lang.com/?script=rJLfavMwDMXv_RR6gYbvo3ce7FWG...

(I don't like to self promo on competitor posts, but since Mermaid doesn't compete in making its own layout engine I felt sharing this under this thread is relevant to HN. If anyone from Mermaid finds it in poor taste just let me know and I'll delete)

Is it possible to visualize PlantUML? I tried to paste some but it wasn’t very easy on mobile.

I tried TALA and am surprised to learn it embeds a machine learning model. I settled on ELK (very complex and time consuming to get right), before getting interested in constraint based graph layout (mostly for aligning nodes). Symmetry is nice to have too.

In fact what I'm trying to do is generating beautiful flow graph illustrations like this (non-sensical, just to give you a vibe):

https://th.bing.com/th/id/OIG4.sqo88280g1BDb7r2aORg?pid=ImgG...

Tis hard. Graph layout (bites fist). Layout based image diffusion (tears). One day though.

Wondering where the machine learning model comes into play? Googling doesn’t seem to bring me to an article and the terrastruct site doesn’t mention it as far as I can see.

Hi! I'm Dominic from the Mermaid product team. You raise some good points here. We released the whiteboard to help users get an exact layout they'd like, but it's in its early stages and is undergoing a lot of improvements.

I understand that automatic layout algos is one of the big draws of Mermaid since it creates a lot of speed, but our current layouts can get a little convoluted. I like your idea on creating a machine learning model, but I'm curious what your biggest pain points are or if you have any basic requirements for a readable and aesthetic diagram. Is it made with hard corners on edges? Rounded?

Would love to hear any thoughts you might have on this! You can email me at dominic@mermaidchart.com if you'd be willing to share. Thanks for your comment!

I have been using the beta and would certainly appreciate a few more layouts. You can have a look at yEd for inspiration. Otherwise, it looks very promising!

I think the main reason why diagrams are not used as often as they should to document code bases is that we developers have to face opposite yet complementary approaches: text based graph specifications (but then the layout's quality doesn't scale with graph size), or GUI based approaches that lead to way better results but are too costly to maintain.

The idea of using machine learning is just a kind of knee jerk reaction to this fact. Maybe we could just throw graphs at a graph neural network and have the model learn all the features we are interested in without listing them explicitly (let alone the rules to decide which to prioritize). It's more an art than a science, really.

Among those listed in these papers[1][2] those I am the the most interesting in, beyond the usual overlap minimization, edge crossing and edge length reduction are the following:

    symmetry/alignment
    hierarchical layouts (subgraphs within nodes)
    Fine-grained control of flow direction (doesn't have to be the same in each subgraph)

Those are the features that have constrained the most my search for a diagram engine. Aesthetics (I mean readability) is paramount to using diagrams as documentation IMO. They are not just graphs, they are mental palaces.

A palace's layout must not change if you decide to build an extension. Stability isn't guaranteed with most graph layout algos: add a node and you might end up with a graph that doesn't look like the previous version. Nodes shifts, edges move around. Confusing. There has been research in this direction[3], namely "interactive graph layout". It forces us to move away from a stateless approach to graph generation (graph specification -> picture) and into a stateful paradigm where the previous state of the layout will be preserved to some extent in the new version. With the layout specified as a mixture of previous layout state + constraints I could picture a pipeline where an LLM watches the commit log of some git repo and updates diagrams via semantic reasoning automatically with a 90% success rate, while the remaining 10% is left to the developer to fix.

And there is also "UI-bility". A high degree of customization, being able to plug your own (react,vue,whatever) components into a graph can turn it into a monitoring tool. I wrote an (incomplete) debugger for a go-style channel framework that displays interactions as sequential diagrams, and, although neither D2 nor PlantUML offer this, I had to give up on using the former because it did not provide on-hover tool-tips, which was critical for my use case.

[1] https://nrl.northumbria.ac.uk/id/eprint/16689/1/survey_graph...

[2] in particular chapter 6, https://repository.library.northeastern.edu/files/neu:4f196k...

[3] https://rtsys.informatik.uni-kiel.de/~biblio/downloads/paper...

Re: mental palaces and interactive diagrams, what is your take on Ilograph?

I am working on a diagramming tool that has the combination of a syntax for diagramming as code, extended with a syntax to define rendering constraints (e. g. this part of the diagram shoukd be left of this part, or this arrow must not cross this arrow). I hope this will greatly ease consistent diagram rendering and also getting the final mile pixel perfect.

Currently already have a very alpha version working of the renderer using Cassowary, and working on making a good GUI.

You lost me at Create your account. I would just want to play with the editor and store in the local browser storage until I decide I like it.

Nice! I love how mermaid keeps getting better!

For sequence-diagrams, nothing beats https://sequencediagram.org/ (I am not connected with them in any way, just a happy user)

Agreed. I’ve tried other editors but so far I’ve always come back to sequencediagram.org — it just works, low fuss.

sequencediagram.org is using PlantUML I believe, so you can do these locally without their website.

I've used this in the past for collaborative diagramming sessions and love its ease and simplicity, but the point of Mermaid is its portability - ie. can be embedded in Markdown docs and viewed in various editors/platforms.

Thanks @maho! We're hoping to keep the improvements flowing. I'm non-technical but from my perspective I thought Mermaid sequence diagram functionality really shines! Would love to fill the gap in my knowledge. What is better about https://sequencediagram.org/ than Mermaid sequence diagrams?

FWIW, I find MermaidChart's sequence diagram editor better than the sequencediagram.org one!

I understand that it is different philosophy but I really would like to see the day when I can use Mermaid inside latex. Or at least get some robust mermaid to tikz converter. That would make my life much easy when preparing slides. I understand that exporting to PNG/JPG can work but usually you lose a lot of customization and you only know can make be bigger or smaller to fit the page.

I was exploring this yesterday and actually came acorss the new GUI that is being introduced in this submission. I ended up exporting to PNG and suffer with fitting it inside beamer page layout.

With Draw.io embedding Mermaid diagrams and plug-ins available for VSCode and other IDEs, why is this so special?

Competition is good for innovation and choice is good for everyone. Does it need to be special?

Hi! I'm Akshatha from the Product team at Mermaid Chart :)

While Draw.io's integration with Mermaid and the availability of plug-ins for VSCode and other IDEs are great, they primarily support programmatic editing of diagrams. What sets Mermaid Chart apart is its bi-directional editing capability. You can edit the code to update the diagram and make changes directly to the diagram, which will automatically reflect in the code.

Currently, this two-way editing functionality is available for class diagrams and flowcharts, but we're excited to expand it to other popular diagram types in the future. Stay tuned!

Heads up: the "Theme Customization in Toolbar" image isn't rendered.

Thanks for sharing!

Thanks, I uploaded it!

The project itself is cool, but I'm doubtful on the philosophical side.

Mermaid aspires to be the Markdown of diagrams, so being editable and consumable via plaintext is paramount. If I have to use a visual editor, why not fetch for more powerful tools and be liberated from the limiting format?

This is akin to a WYSIWYG Markdown editor (which to be fair has a niche market). I would ask why not just use Google Doc or MS Word at that point?

I used this recently as someone shared a link to a diagram at work and I edited it for my own comprehension. It's nice. I'd prefer to have this in VSCode tho!

On a related subject, is there a tool to read code and generate Mermaid class diagrams, and, maybe, vice-versa?

That's pretty cool. Wish PlantUML community would have something like it.

Do Mermaid class diagrams support generics (parameterized types)?

Yes

> … though generics that include a comma are currently not supported. [1]

So yes-ish, only in the most basic way.

[1] https://mermaid.js.org/syntax/classDiagram.html

Is there a demo available without creating an account?

Yes! You can use this in the free mermaid playground: https://www.mermaidchart.com/play

Finally. I am not fond of code-to-diagram tools and wanted to try Mermaid, as it seems like one of the better diagramming tools around. Will definitely give it a try now.

This is great and all, but this would better be served as a desktop app with lower overhead.

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