How it works
Select a template from the dropdown menu to get started. The editor will populate with sample code for that diagram type.
You can then modify the text to customize the diagram to your needs. The preview updates instantly.
Diagram Viewer
Build sequence diagrams, flowcharts, or Gantt timelines using guided templates and instant previews.
Updated Dec 06, 2025
Visual Documentation
Create diagrams from text definitions
The Diagram Viewer is a versatile tool for creating various types of diagrams using simple text definitions. It supports Flowcharts, Sequence Diagrams, Class Diagrams, State Diagrams, Gantt Charts, and Pie Charts.
Supported Types
Visualize processes with Flowcharts, show interactions with Sequence Diagrams, or model systems with Class Diagrams.
Plan projects with Gantt Charts and track states with State Diagrams.
Flowcharts
Visualize processes and workflows.
Sequence Diagrams
Show interactions between objects over time.
Class Diagrams
Model the structure of a system.
Gantt Charts
Plan and schedule projects.
Popular combinations
- Audit with Diff Checker
Compare Diagram Viewer output with previous revisions to avoid regressions.
- Share via QR Code Generator
Turn sanitized payloads into QR codes for offline reviews.
Frequently asked questions
What kind of diagrams can I build?
The Diagram Viewer supports a wide range of visual structures, including flowcharts, sequence diagrams, class diagrams, state charts, and Gantt charts.
Do I need to know coding?
It depends. While some diagram types use a code-based definition (like Mermaid), others might offer a more visual approach. This viewer is designed to help you visualize code-defined diagrams instantly.
Can I save my diagrams?
Currently, diagrams are rendered in real-time. We recommend saving your source code (text definition) locally. We are exploring cloud storage options for future updates.
Is it compatible with other tools?
Yes. The syntax used is often compatible with popular tools like Mermaid.js, making it easy to move your diagrams between different platforms.
How to use Diagram Viewer
Follow these four quick steps to inspect markup or diagrams with instant previews right inside your browser—no downloads, no accounts, and no data leaving the FreeTools.run sandbox.
Step 1: Load your source data
Paste text, drag a file, or start with our curated sample to understand how the viewer workflow behaves with real inputs.
Step 2: Adjust tool options
Toggle presets, update formatting rules, or choose export preferences. All controls update in real time so you can preview the effect before committing.
Step 3: Review the live preview
Use the split-pane preview, inline validation, or diff output to confirm the transformation looks correct before you copy anything back into your project.
Step 4: Export or chain another tool
Copy the result, download a file, or jump into a related FreeTools.run utility (like Diff Checker or the QR Code Generator) to continue the workflow without leaving the browser.