Stable rendererSequenceMermaidAPI flows

Sequence Diagram Preview

Use Mermaid sequenceDiagram syntax to preview API calls, login flows, payments, and service interactions.

Examples

Detected Mermaid

This input may work better in the matching tool. Open Mermaid tool

Sequence diagram text

Rendered sequenceReady

Your sequence diagram will appear here.

Continue with a related tool

Move this preview into a nearby workflow for conversion, debugging, or export.

AI Diagram Generator

Generate Mermaid diagrams from a natural language prompt with AI.

Open

Mermaid AI Fixer

Fix broken Mermaid syntax and improve diagram readability with AI.

Open

Architecture Diagram Generator

Generate Mermaid architecture diagrams from product or system notes with AI.

Open

How to use

1Paste Mermaid sequenceDiagram syntax.
2Start from API, login, or payment samples.
3Export the rendered SVG or PNG.

Common use cases

API documentationAuth flowsPayment flows

Related tools

AI Diagram Generator

Generate Mermaid diagrams from a natural language prompt with AI.

Mermaid AI Fixer

Fix broken Mermaid syntax and improve diagram readability with AI.

Architecture Diagram Generator

Generate Mermaid architecture diagrams from product or system notes with AI.

FAQ

Which syntax does this tool use?

It uses Mermaid sequenceDiagram syntax and the Mermaid browser renderer.

Sequence Diagram Preview is a focused editor for message flows between users, apps, services, databases, and external systems.

Because it uses Mermaid sequenceDiagram syntax, the source can live naturally in Markdown files, code review comments, and architecture notes.

Use the page for API call flows, login journeys, payment systems, and AI-generated interaction diagrams.

Demo: preview an API request sequence

Sequence diagrams are best when they show responsibility, not every internal function call. A focused preview helps reviewers confirm who calls whom and what the important return values are.

Show external users or systems as explicit participants.
Use notes for assumptions rather than adding fake service calls.
Add alt blocks for failure paths that need operational handling.

sequenceDiagram
  participant Browser
  participant API
  participant DB
  Browser->>API: POST /orders
  API->>DB: insert order
  DB-->>API: order id
  API-->>Browser: 201 Created

Debugging: keep Mermaid sequence syntax small

When a sequence diagram breaks, simplify it to participants and one message. Then restore loops, alternatives, and notes after the renderer accepts the base flow.

Declare participants when labels contain spaces or punctuation.
Keep arrows consistent for request and response messages.
Avoid mixing flowchart syntax inside sequenceDiagram blocks.

sequenceDiagram
  participant Web App
  participant API
  Web App->>API: health check
  API-->>Web App: ok

Review checklist for Sequence Diagram Preview

Use Sequence Diagram Preview when you need to inspect source content visually before it becomes documentation, a pull request note, an incident write-up, or a handoff artifact. Preview sequence diagrams from Mermaid sequenceDiagram syntax.

Before exporting, check that labels are readable, relationships match the source, generated examples do not contain private data, and the preview still makes sense after you edit the input.

Limits and troubleshooting

If the preview fails, reduce the input to the smallest complete example, confirm the format syntax, and then add sections back one at a time. Many rendering failures come from partial files, indentation mistakes, missing diagram headers, or copied snippets that depend on hidden context.

Treat the preview as a review surface rather than a source of truth. Generated diagrams, converted files, dashboards, and rule examples should be checked before they are used in production documentation or operations.

Example inputs to test

API call: sequenceDiagram participant Client participant API participant DB Client->>API: GET /diagrams API->>DB: Query diagrams DB-->>API: Rows API-->>Client: JSON
Login flow: sequenceDiagram participant User participant App participant Auth User->>App: Enter credentials App->>Auth: Verify Auth-->>App: Token App-->>User: Dashboard
Payment flow: sequenceDiagram participant Buyer participant Store participant PSP Buyer->>Store: Checkout Store->>PSP: Create payment PSP-->>Store: Confirmed Store-->>Buyer: Receipt

Tool maturity

Stable renderer

Stable tool

This tool has a dedicated renderer or preview surface, useful exports, and a repeatable browser-first workflow.

The maturity label is not a quality score. It tells visitors whether the tool is best for stable export, deeper debugging, quick parsing, or AI-assisted generation.