PlantUML Web MCP Server

Overview

The plantuml_web MCP server bridges the gap between AI assistants and PlantUML diagram generation. By exposing PlantUML’s rendering capabilities through the Model Context Protocol, developers can let AI agents generate, validate, and refine UML diagrams directly from natural language prompts. This eliminates the need for manual diagram editing or external tooling, enabling seamless integration into documentation workflows, code reviews, and knowledge‑base creation.

What Problem Does It Solve?

Creating accurate UML diagrams often requires a dedicated editor and a separate rendering step. AI assistants traditionally lack direct access to such visual tooling, forcing users to copy generated PlantUML code into a separate editor. The plantuml_web MCP server resolves this by providing an API that accepts PlantUML source, returns rendered images (SVG or PNG), and validates syntax—all over a single SSE endpoint. This eliminates context switching, reduces errors, and speeds up iteration cycles when AI agents need to produce or update diagrams on the fly.

Core Functionality and Value

At its heart, the server offers two primary tools:

• – Transforms PlantUML text into a rendered image, returning the binary data and MIME type. This lets an AI assistant embed diagrams directly in chat or documentation outputs.
• – Checks the PlantUML code for errors, providing detailed messages that can be fed back to the user or used by an AI model to auto‑correct syntax.

Because the server runs on a lightweight Java backend (PlantUML jar) behind a NiceGUI web interface, it is both fast and easily deployable on intranets or cloud environments. Developers can host the MCP server in a Docker container, exposing ports for the web UI and the SSE endpoint, or run it natively with a simple script.

Key Features

• Live rendering – The NiceGUI frontend offers an interactive editor with real‑time preview, allowing quick visual feedback before sending code to the MCP server.
• Format flexibility – Images can be requested as SVG (scalable vector graphics) or PNG, catering to different use cases such as embedding in PDFs or web pages.
• Error transparency – Validation returns structured error messages, enabling AI assistants to present clear guidance or automatically correct malformed diagrams.
• Responsive UI – Resizable panels and a clean layout make the web interface usable on both desktop and mobile devices, useful for developers working remotely or in constrained environments.

Use Cases

• Documentation generation – AI assistants can automatically produce class or sequence diagrams from code comments, then embed the rendered images in Markdown files.
• Code review support – During pull requests, an assistant can generate updated UML diagrams reflecting new code changes and present them inline in the review discussion.
• Educational tools – Instructors can ask an AI to explain system architecture by generating diagrams on demand, reducing the overhead of manual diagramming.
• Rapid prototyping – Designers can iterate on system models quickly, letting the AI suggest diagrammatic changes and immediately visualizing them.

Integration into AI Workflows

Once added to an MCP‑enabled client (e.g., Claude Desktop), the server’s tools become first‑class actions. An assistant can call after interpreting a user’s request, then return the image as part of its response. The validation tool can be used in a loop to refine code until it passes syntax checks, providing a smooth developer experience. Because the MCP interface is stateless and uses Server‑Sent Events for streaming, latency remains low even when rendering complex diagrams.

Standout Advantages

• Zero‑configuration Java dependency – The PlantUML jar is bundled, so users need not install a separate JVM or manage classpaths.
• Dual‑purpose interface – The same deployment serves both a user‑friendly web editor and an AI‑ready API, simplifying operations.
• Open‑source and community‑driven – Built on NiceGUI, a popular lightweight framework, ensuring future compatibility with other MCP servers and tools.

In summary, plantuml_web transforms PlantUML from a standalone rendering tool into an AI‑accessible service, streamlining diagram creation and validation within modern development pipelines.