An entity-relationship diagram (ERD) is the standard way to design and document a relational database before you write a single line of SQL. It shows the entities (tables) in your system, the attributes (columns) each one holds, and — most importantly — the relationships between them: which tables reference which, and whether a row in one maps to one or to many rows in another. This free ER diagram maker lets you build that picture visually in the browser, so you can think through a schema, agree on it with your team, and keep it as living documentation, without installing dbdiagram, Lucidchart, or a desktop modelling tool.

Getting the relationships right is the entire point of an ERD, because that is where database designs succeed or fail. A one-to-many relationship (one customer has many orders) becomes a foreign key on the 'many' side. A many-to-many relationship (students enrol in many courses, courses hold many students) needs a join table — and an ERD makes that obvious before it becomes a painful migration. By drawing entities and connecting them visually, you catch missing keys, redundant columns, and normalisation problems while they are still cheap to fix, rather than after the schema is in production.

The tool produces clean Mermaid ER diagram code as its output, which is what makes it genuinely useful for developers rather than a throwaway picture. Mermaid is text-based diagram syntax that renders natively in GitHub, GitLab, Notion, Obsidian, VS Code, and most modern documentation platforms. That means your ERD lives in your README or wiki as code: it version-controls cleanly, shows up in diffs when the schema changes, and never goes stale the way an exported PNG does. Design the diagram here, copy the Mermaid block, and paste it straight into your project docs.

An ERD is also the fastest way to onboard anyone onto an existing system. A new engineer can understand a database from one good diagram far quicker than by reading dozens of CREATE TABLE statements, and a product or data stakeholder can follow the relationships without knowing SQL at all. Keeping an up-to-date entity-relationship diagram next to your schema — for a SaaS data model, an e-commerce catalogue, a CRM, or any app with more than a handful of tables — pays for itself the first time someone new has to reason about how the data fits together.

Because everything runs client-side, there is no account, no upload, and no limit: you sketch the schema, export the code, and move on, and your data model never leaves your browser. That privacy matters when the schema you are designing is for an unreleased product or an internal system you would rather not paste into a third-party SaaS modelling tool. For deeper modelling work, the diagram pairs naturally with the other developer tools on this site — a UML diagram tool for class and sequence diagrams, a SQL formatter for the DDL you write from the design, and a JSON tool for the API shapes the database will serve.