Mermaid Renderer

Validate and render Mermaid diagram syntax for flowcharts, sequences, ER diagrams, and more.

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Input
Output
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About mermaid renderer

Mermaid Renderer loads once and then runs on its own. Close the tab and there is nothing left behind, on the machine or anywhere else.

No telemetry, no analytics on what you type, no request that carries the contents anywhere. The browser does the whole job.

You will find it under Diagrams, alongside 9 other tools for the same sort of job.

Detects diagram type and reports syntax errors.

How to use it

01
Start it
Every control is on the tool itself. Keyboard shortcuts, where there are any, are listed beside it.
02
Watch it run
It updates in the page as you go. Nothing is sent anywhere, so it keeps working with the network off.
03
Close when done
Nothing is stored between visits. Reloading gives you a clean start rather than picking up where you left off.

Examples

Render Flowchart
Render a Mermaid flowchart diagram
Input
graph TD
    A[Start] --> B{Decision}
    B -->|Yes| C[OK]
    B -->|No| D[Cancel]
Output
graph TD
    A[Start] --> B{Decision}
    B -->|Yes| C[OK]
    B -->|No| D[Cancel]
Render Sequence Diagram
Render a Mermaid sequence diagram
Input
sequenceDiagram
    Alice->>Bob: Hello
    Bob-->>Alice: Hi back
Output
sequenceDiagram
    Alice->>Bob: Hello
    Bob-->>Alice: Hi back

Questions

Does Mermaid Renderer work offline?+

Yes. It is JavaScript running in this tab, so once the page has loaded it needs nothing further from the network. Put the machine in flight mode and it carries on. Nothing you do here is sent anywhere, because there is nowhere for it to go.

Does it remember anything between visits?+

No. Reload the page and it starts from nothing. There is no account, no saved state and no cookie holding your last session. That is a deliberate trade: it cannot lose your data because it never keeps any.

Is it accurate?+

Timing comes from performance.now(), the high resolution clock the browser provides, rather than from setInterval, which drifts by a few milliseconds every tick and compounds over minutes. What can still shift things is the browser throttling a tab in the background, so leave it visible if the timing matters.

Does it make a sound?+

Where a sound makes sense, it is generated with the Web Audio API rather than loaded as a file, so there is nothing to download and nothing to block. Browsers refuse to start audio until you have interacted with the page, which is why the first press is what switches it on.

Can I use Mermaid Renderer on a phone?+

Yes. The controls are sized for touch and the layout collapses to one column on a narrow screen. Bear in mind that a phone locking its screen will suspend the page, and timing stops with it.