Viaduct

Viaduct

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Compared

Viaduct vs IcePanel

Both are visual C4 modelling tools you open in a browser rather than DSLs you write. They differ in what the free tier holds, and in what sits on an element: IcePanel is built around collaborative design of the model itself, while Viaduct keeps the documentation, the API contracts and the data flows on the elements and serves all of it to coding agents over MCP.

01What it is

IcePanel, fairly

IcePanel is a collaborative diagramming and modelling tool with an easy-to-use interface, an API and SDK, and an MCP integration for keeping a model updated — the description its entry on c4model.com gives. Its free plan is meant for a solo developer or a small team: one editor, unlimited viewers, up to 100 model objects and one flow per diagram.

icepanel.io/pricing

02Side by side

Where they differ

Figures taken from each vendor’s own pages, October 2026.
 ViaductIcePanel
Free tierEverything, with an account: all four levels, flows, documentation, collaboration, change sets and the MCP server. No cap on editors or elements.1 editor, unlimited viewers, up to 100 model objects, 1 flow per diagram.
Paid plansOnly the desktop app — €10 a month after 7 free days, one licence for three machines.Growth $40 and Scale $80 per editor per month, billed annually.
DocumentationMarkdown and PlantUML sequence diagrams attached to the element they describe.Decision records on the Growth plan and upwards.
API contractsEndpoints, broker channels, ER tables, OpenAPI and Protobuf schemas modelled on the element itself.Not part of the model; linked out to.
AI coding agentsA hosted MCP server with scoped tokens, plus a REST API and webhooks.MCP and API integrations, with API usage tiered by plan.
Runs on your own machineDesktop app with local JSON files and an MCP server on localhost; the Community edition is open source.Hosted, with single-tenant and data-residency options on Enterprise.

Plans and prices move. Before deciding, read them at icepanel.io/pricing and on our own pages.

03The decision

Which one to pick

Choose IcePanel if

  • You need enterprise controls now — SSO domains, audit logs, data residency, a single-tenant environment.
  • Large-model navigation features like domains and overlays are what you are paying for.
  • Your organisation already runs on it and the model is where the team looks.

Choose Viaduct if

  • More than one person has to edit, and a one-editor free tier is the wrong shape for that.
  • The contracts belong in the model — endpoints, channels, schemas, not links to them.
  • Agents are part of the team: the model is read and written over MCP as work happens.
  • The architecture has to be able to live on your own machine as files you own.

04Questions

Asked about this pair

Is Viaduct free, and what is the catch?

The browser edition is free with an account, and that includes every C4 level, documentation, Magic flows, collaboration, change sets and the hosted MCP server. There is no editor cap, no element cap and no trial clock. The paid product is the desktop app, which runs on your own machine and keeps projects as JSON files.

How many people can edit a model for free?

In Viaduct, as many as you invite — the free browser edition does not meter editors or model elements. IcePanel’s free plan allows one editor with unlimited viewers, and paid plans are priced per editor. Check both current pages before deciding; plans change.

Can I move a model between the two?

There is no direct import either way. Viaduct exports JSON, PlantUML, PNG and SVG, and its REST API can be read element by element, so a rebuild is scripted work rather than retyping. Both tools follow the same four C4 levels, which is what makes that possible at all.

What a C4 modeling tool is Viaduct vs Structurizr

Try it before you compare further.

The browser edition is free with an account — all four levels, the documentation, the flows and the MCP server, with nothing held back for a paid plan.

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