For many teams, software diagrams used to live in a separate world from the code they described. A design changed in Git, but the architecture image stayed in a slide deck. A workflow changed in an API, but the flowchart remained in a wiki page that nobody wanted to edit. Diagram-as-code fixes this gap by making diagrams plain text that can be reviewed, versioned, and updated with the rest of the project.
Mermaid is one of the most approachable diagram-as-code tools because its syntax feels close to Markdown. You can write a flowchart or sequence diagram in a few lines, render it in a browser, and keep the source beside the documentation it supports.
Diagram-as-code means describing a diagram with text instead of drawing it manually on a canvas. A rendering engine reads the text and produces the visual layout. In Mermaid, a basic flowchart can be as small as this:
flowchart LR Idea[Product idea] --> Design[Technical design] Design --> Build[Implementation] Build --> Review[Code review] Review --> Release[Release]
The source is short enough to paste into a pull request, update during review, and store in the same repository as the code. That is the core shift: the diagram becomes maintainable documentation, not a detached image.
Diagram-as-code is strongest when the diagram explains logic, communication, state, or structure. It is especially useful for documentation that changes with code:
It is less ideal for highly polished marketing illustrations, dense visual maps, or diagrams where exact manual placement is more important than maintainability. In those cases, a design tool may still be the right choice.
Mermaid.js has become popular because it is readable, embeddable, and widely supported across developer documentation workflows. It supports common diagram types including flowcharts, sequence diagrams, class diagrams, ER diagrams, state diagrams, and Gantt charts.
For teams that already write documentation in Markdown, Mermaid is a natural fit. A diagram can sit directly below the paragraph it explains, and the source remains visible to future editors.
You do not need to convert every diagram at once. Start with diagrams that frequently become stale. A good first target is an API flow, an onboarding flow, or a release workflow that engineering and product teams both reference.
Imagine a team wants to document how a pull request moves from draft to production. The Mermaid source can capture the lifecycle without a separate drawing file:
stateDiagram-v2 [*] --> Draft Draft --> ReadyForReview: mark ready ReadyForReview --> ChangesRequested: reviewer comments ChangesRequested --> ReadyForReview: update branch ReadyForReview --> Approved: approval Approved --> Merged: merge Merged --> Released: deploy Released --> [*]
This diagram is easy to change when the team adds a QA gate or deployment approval. The review diff shows the process change directly.
Mermaid syntax is readable, but it is still faster to learn with immediate feedback. Mermaid Preview gives you a live editor, starter templates, SVG and PNG export, and shareable compressed links. That makes it a useful drafting space before you paste the final source into Markdown.
Try this in Mermaid Preview: paste the examples into the live editor, adjust the labels, then export SVG or PNG for your docs.
Open Mermaid Preview →