Diagram as code studio

Open the diagram files Apple devices show as plain text.

Diagrammar renders Mermaid, PlantUML, D2 and Graphviz DOT as native views on iPhone, iPad and Mac. No WebView, no JavaScript runtime, no network. Viewing every format is free.

Download on the App Store

Four formats 27 templates Works offline

A rendered Mermaid sequence diagram of an OAuth 2.0 flow on iPad, with participants App, Browser, Auth and API across ten numbered steps.
iPad · OAuth 2.0 sequence diagram, rendered natively
A PlantUML single sign on sequence diagram rendered on iPhone in PlantUML's own default theme.
iPhone · a .puml, in PlantUML's own theme palette

The problem

Someone sends you a .puml. Your phone offers to open it in a text editor.

Diagram code is plain text, so every Apple device happily shows you the source and none of them show you the diagram. The viewer apps that do exist handle Mermaid only, and most of them are a browser engine in a trench coat: they need a network, they break when the bundled JavaScript goes stale, and they look nothing like the tool that produced the file.

Four formats

Mermaid, PlantUML, D2 and Graphviz DOT. The format is detected from the content, so pasted code renders without picking one first.

Layout that holds up

A clustered graph keeps its clusters instead of collapsing into a tangle of crossed lines, and a wide diagram stays wide.

Nothing to load

Everything renders on your device, so there is nothing to download and no request leaving your phone.

Formats

Four formats, four parsers.

Every format gets its own grammar, and each renders in the theme palettes you already recognise from the desktop tools.

.mmd · .mermaid

Mermaid, in Mermaid's own themes

Flowcharts, sequence diagrams, state machines, class and ER diagrams, git graphs and mindmaps. The official Forest, Neutral and Base theme palettes are here, so the colours match the ones your docs already use. Chart shaped types such as pie, Gantt, timeline and radar are drawn as real charts, not pictures of charts.

A Mermaid CI and CD pipeline flowchart with a rollback branch, rendered on iPhone in the official Mermaid Forest theme.
CI pipeline · Mermaid Forest theme
.puml · .plantuml · .iuml

PlantUML, which nothing else on iOS opens

Sequence diagrams, class diagrams with inheritance and composition, activity diagrams and use case diagrams, drawn in PlantUML's own default and dark themes.

A PlantUML sequence diagram of a single sign on exchange between user, app, identity provider and sessions, on iPhone.
Login sequence · PlantUML Default theme
.d2

D2, containers and all

D2's nested containers stay nested, along with styled shapes, database tables and classes. Multi tier architecture diagrams keep their grouping instead of collapsing into a flat graph.

A D2 multi tier platform architecture on iPad, showing CDN, load balancer, an API tier of three services and a data tier, drawn as nested containers.
Platform architecture · nested containers on iPad
.dot · .gv

Graphviz DOT, clusters intact

Pipe terraform graph into a file and open it on your iPad. Clustered graphs keep their clusters, and you can switch the layout to see the same graph arranged several different ways.

Output of terraform graph rendered on iPad as a clustered Graphviz diagram showing AWS VPC, subnets, security groups and instances.
terraform graph output · clustered DOT on iPad

Someone sends you a diagram file. You open it on the train, with no signal, and every node, edge and label is there, laid out and legible.

What you get

A reader that never asks for money, and an editor when you want one.

Open a whole README and read it properly

Markdown mode renders an entire .md file with every fenced mermaid, plantuml, d2 or dot block drawn inline, prose in between, exactly where the author put it. Tap any diagram to open it full size.

  • Headings, lists and code, with diagrams in place
  • Every fenced format renders, not just Mermaid
  • Any diagram expands to a full screen sheet
A Checkout Service README on iPhone with prose, a bulleted list and an inline rendered sequence diagram between the sections.
Markdown mode · a real README, diagrams included

Your diagrams get drawn in the Files app

Diagram files show a rendered thumbnail of the actual diagram wherever files are listed, so a folder of .mmd and .dot files stops being a wall of identical text icons. On the Mac you get full Quick Look from the Finder as well. Both are free.

  • Rendered thumbnails on iPhone and iPad
  • System wide Quick Look on macOS
  • Files and iCloud Drive, with autosave
The Files browser on iPad showing eight diagram documents — Binary Search, dbt Lineage, Kubernetes Topology, Login Sequence, OAuth 2.0 Flow, Order Lifecycle, Platform Architecture and Terraform Graph. Seven show a rendered thumbnail of their own diagram as the file icon; Terraform Graph shows a generic DOT file icon.
Files on iPad · seven of eight files rendered as their own icon

Rearrange the diagram without touching the source

Change flow direction, edge routing and layout algorithm from one sheet and watch the diagram re lay out. The same source becomes a top down flow or a left to right one, with orthogonal or curved connections, without editing a line.

  • Four directions, five edge routing styles
  • Five layout arrangements to switch between
  • System, Light, Dark and the full theme catalogue
The Display sheet on iPhone showing Format, Theme, Direction and Connections controls above a Mermaid CI pipeline diagram.
Display sheet · format, theme, direction, connections

Get it out again as something you can send

Export PNG or PDF, print, or copy the rendered diagram straight to the clipboard for a ticket or a slide. Select diagram code in any other app and the share sheet renders it without opening Diagrammar and finding the file first.

  • PNG and PDF export, and print
  • Copy as image, straight into a ticket
  • Share extension from any app
The export menu open over an OAuth sequence diagram on iPhone, offering Export PNG, Export PDF, Copy as Image and Print.
Export · PNG, PDF, copy as image, print

How it works

It starts with a file you already have.

Open the file

From Files, iCloud Drive, a share sheet or the Finder. Or start from one of 27 templates covering all four formats.

Diagrammar detects the format

The format is detected from the content, then parsed and laid out on your device. Nothing is sent anywhere.

Read it, change it, send it

Pinch and pan, tap a node, switch the layout, then export a PNG or PDF when someone needs a picture instead of a file.

Pricing

Viewing is free. Authoring is the paid part.

There is no paywall between you and a diagram someone sent you. Charging someone to look at a file they did not ask for would sell nothing and help no one.

Diagrammar

Free

Everything you need to read a diagram anyone sends you.

  • Open and view all four formats
  • Pan, zoom and tap any element
  • Rendered thumbnails in Files
  • Quick Look on macOS
  • System, Light and Dark themes
  • Template gallery, layout controls
  • Files and iCloud Drive
Download free

No account and no trial timer.

Diagrammar Pro

$14.99 once

For the times you are writing the diagram, not just reading it.

  • Edit every format, DOT included
  • Export PNG and PDF, print, copy as image
  • Markdown mode for whole READMEs
  • Share extension from any app
  • Every theme, including each format's own
  • Syntax problems flagged with line numbers
  • One purchase covers iPhone, iPad and Mac
Get Pro — $14.99

One time purchase. It does not renew.

The Diagrammar Pro sheet on iPhone, headed "Export this diagram" and "Included in Diagrammar Pro, with everything else below", above a small rendered flowchart and a feature list covering export, editing every format, Markdown mode, the share extension and the full theme catalogue.
The Pro sheet, exactly as it appears in the app

Questions

What to know before downloading.

Is this a WebView wrapper around mermaid.js?

No. Diagrammar reads the diagram source and lays it out with a real layout engine, then draws it directly on screen. There is no WebView, no JavaScript runtime and no bundled browser anywhere in the app. That is why it opens instantly, works with no signal and never shows you a half loaded diagram.

Is this just another Mermaid viewer?

Mermaid is one of four formats. Diagrammar also opens PlantUML, D2 and Graphviz DOT, each with its own layout engine. If you only ever open Mermaid files, other apps will serve you. If you have a .puml or a .dot sitting in a repo, this is the only native option.

What is free and what costs money?

Viewing is free and always will be. Every format opens, renders, pans, zooms and shows rendered thumbnails in Files at no cost. Pro unlocks authoring: editing every format, PNG and PDF export, printing, Markdown mode, the share extension and the full theme catalogue.

Is Pro a subscription?

No. Diagrammar Pro is a one time purchase of $14.99. There is no subscription, no account to create and nothing that expires.

Does it work offline?

Yes. Everything renders on device. Nothing is sent to a server, so a runbook opens on a plane, in a datacentre or at 3am on a train exactly as it does at your desk.

Will my diagram look exactly like it does on my desktop?

No. Diagrammar is a native rewrite rather than the original renderer ported over, so type, spacing and some styling will differ from mermaid.js or PlantUML, and a few format specific constructs are still unsupported.

What it does guarantee is structure. Every node, edge, label and relationship is preserved, and layout runs through a real layout engine. Theme palettes are supported, so Mermaid Forest reads as Mermaid Forest. Malformed source produces a readable error with the line number instead of a blank screen. And because viewing every format is free, open your own files and judge for yourself before spending anything.

Does it work on Mac?

Yes, from one app covering iPhone, iPad and Mac, with one purchase for all three. On the Mac you also get system wide Quick Look, so diagram files preview from the Finder without opening the app at all.

Which diagram types are supported?

Flowcharts, sequence diagrams, state machines, class diagrams, ER diagrams, git graphs and mindmaps, plus D2 containers and clustered Graphviz graphs. Chart shaped Mermaid types, meaning pie, Gantt, timeline, xychart, quadrant, radar and journey, are drawn with real axes and scales.

Where are my files stored?

Wherever you already keep them. Diagrammar opens plain text files straight from Files and iCloud Drive. It stores nothing of its own, so your diagrams stay in the formats and folders you use now, readable by every other tool you own.

What about visionOS and Apple Watch?

Neither ships today. The groundwork is in place and the platform is planned for a later release. Apple Watch is not planned, because a diagram that fits on a watch is not usually worth drawing.

Who makes Diagrammar?

Silkway Studio, a small studio building native software for Apple platforms. Diagrammar is powered by DiagramKit, the studio's diagram rendering SDK, which is also licensed to other developers.

Get Diagrammar

Open the file you were sent.

Free on iPhone, iPad and Mac. Every format renders without paying anything, so you can check your own diagrams before you decide about Pro.

Download on the App Store

No account No network required One time purchase for Pro

iPhone, iPad and Mac · iOS, iPadOS and macOS 26.5 or later.