Diagram & Flowchart Editor

Diagram & Flowchart Editor

Create flowcharts, UML diagrams, mind maps visually. Export to SVG/PNG. Free online diagram maker and flowchart creator

A flowchart, sequence diagram, or system architecture sketch is the fastest way to communicate a design — but only if drawing it takes less time than explaining it. Dedicated tools (Lucidchart, Visio, draw.io) are powerful but slow to start; specialized syntax (Mermaid, PlantUML) is faster but needs learning. This editor offers both: visual drag-and-drop for quick sketches AND text-based Mermaid for diagrams you want versioned in git.

When to use which approach

  • Mermaid text syntax — diagrams that live alongside code (in markdown docs, README.md, ADRs). Versioned, diffable, regenerates from source. Best for: flowcharts, sequence diagrams, class diagrams, ER diagrams. Native rendering on GitHub.
  • PlantUML — older, more diagram types. Better for UML purists. Renders on the server.
  • Visual editor (drag-and-drop) — one-off diagrams that need precise positioning or unique styling. Sketches for a meeting; not meant to be versioned.
  • Excalidraw — hand-drawn aesthetic, collaborative real-time. Good for whiteboard-style thinking.
  • Specialized tools — Figma for UI flows, Lucidchart for org charts, MS Visio for IT diagrams in corporate environments.

Working example: a sequence diagram in Mermaid

Input

A user logs in with OAuth via Google

Output

sequenceDiagram
  participant U as User
  participant App as Our App
  participant Google
  participant DB as Database

  U->>App: Click "Sign in with Google"
  App->>Google: Redirect to OAuth consent
  Google->>U: Show consent screen
  U->>Google: Approve
  Google->>App: Callback with auth code
  App->>Google: Exchange code for tokens
  Google-->>App: Access token + ID token
  App->>DB: Find/create user record
  DB-->>App: User row
  App->>U: Set session cookie, redirect to dashboard

GitHub markdown renders this inline:
  ```mermaid
  sequenceDiagram
  ...
  ```

Mermaid in markdown is git-friendly: changes appear as text diffs (which arrow moved, which actor renamed) rather than binary image churn. Lives next to the code it describes; refreshes with the codebase.

Diagram types ranked by usefulness in tech

  • Sequence diagram — interactions across services / actors over time. Most useful for documenting API calls, OAuth flows, distributed transactions.
  • Flowchart — decisions and branches. Useful for business logic, state-dependent flows, request handling.
  • ER diagram (entity-relationship) — database schemas. Useful for explaining data models to new team members.
  • Class diagram — OOP class relationships. Useful in heavy-OOP languages; less common in modern functional-flavored codebases.
  • State diagram — state machines (see also the state-machine-designer tool). Useful for UI flow, order lifecycles.
  • C4 model (Context, Container, Component, Code) — for software architecture documentation. Hierarchical: start broad, zoom in. See also: architecture-diagrammer.
  • Mind map — brainstorming, planning. Less useful for "documentation" than for "thinking".
  • Gantt chart — project timelines. Useful but tedious; project tools (Linear, Asana) usually do this better.

When to reach for this tool

  • You are writing a design doc and need to explain a system flow.
  • You are debugging an issue and want to map "what calls what" to find where it breaks.
  • You are onboarding someone and a diagram saves you 10 minutes of verbal explanation.
  • You are reviewing an architecture and want to verify the proposed design fits together.

What this tool will not do

  • It will not auto-generate diagrams from your code. Some tools do this for class diagrams (analyzing imports / class hierarchies); for sequence diagrams, the dynamic call graph is not statically extractable. Generate manually from the design intent.
  • It will not enforce diagram correctness. The tool draws what you specify; whether the diagram matches reality is your responsibility.
  • It will not collaborate in real-time. For multi-user simultaneous editing, use Excalidraw, Figma, or Lucidchart.
  • It will not produce print-quality output for academic papers. For LaTeX docs, use TikZ or PlantUML with PDF output.

Frequently asked questions

Should I use Mermaid or PlantUML?

Mermaid is rendered natively on GitHub, GitLab, and many static-site generators in 2026 — for documentation in repos, Mermaid wins. PlantUML has more diagram types and finer styling control but requires a separate rendering step. For new projects: Mermaid by default.

Can I export diagrams to PNG/SVG?

Yes — most diagram tools export both. SVG is preferable when the consumer can render it (web, modern docs); PNG is more universal but loses quality on scaling.

How do I version diagrams in git?

For text-based (Mermaid, PlantUML): commit the .mmd / .puml source. Diffs are readable; renders are reproducible. For visual editor exports: commit the JSON / DSL source (most editors have one) plus the rendered image. Avoid committing only the PNG without source — non-editable.

Is draw.io / diagrams.net better than this?

For complex, precisely-styled diagrams with many shape libraries (AWS icons, network gear, BPMN), draw.io is more powerful. For quick diagrams, the browser editor is faster to launch. Use both for different tasks.

Do C4 diagrams need special software?

C4 is a methodology, not a syntax. You can draw C4 diagrams in any tool — Mermaid, draw.io, PlantUML have C4 templates / extensions. The value is in the layered abstraction (Context → Container → Component → Code), not the specific software.

How do I keep diagrams up to date?

Hardest problem in diagramming. Tactics: (1) text-source diagrams in the same repo as the code they describe (easy to update during PRs); (2) generate diagrams from authoritative sources (database schema → ER diagram; OpenAPI → service map); (3) date-stamp diagrams and treat as "as-of" snapshots. Outdated diagrams worse than no diagrams.

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Last updated · E-Utils editorial team