Tool Overview

The ER Diagram Generator turns SQL database schemas into interactive entity relationship diagrams. You paste or upload SQL DDL statements such as CREATE TABLE and ALTER TABLE, and the tool parses tables, columns, primary keys, and foreign keys. It then lays out tables as nodes, draws relationship lines, and lets you export clean diagrams as PNG, JPG, WebP, or PDF.

The problem it solves is clear. Understanding a database by reading raw SQL is slow and error prone. Complex systems have many tables and foreign key relationships. Manually drawing diagrams in graphics tools takes time and must be updated by hand when the schema changes. This generator creates diagrams directly from the real schema and can update them in seconds when the SQL changes.

The tool is designed for developers, database designers, architects, and students. It works for beginners who are just learning database design and want to “see” how tables connect. It also helps professional teams documenting existing systems or planning migrations. The interface gives direct feedback as you change your schema, so you can iterate on design quickly.

Background & Concept Explanation

An ER diagram (Entity Relationship diagram) shows how data entities relate to each other in a database. Each table is an entity. Columns represent attributes. Primary keys identify rows. Foreign keys link one table to another, forming one to many or many to many relationships. Good diagrams help people reason about structure, data flow, and integrity rules.

Relational databases often start as ER designs before any code is written. Over time, real schemas evolve. New tables appear, columns are added or changed, and indexes and views grow around them. Teams inherit systems where documentation is outdated or missing. Reading hundreds of lines of SQL DDL to rebuild a mental diagram is difficult for anyone, even experts.

The ER Diagram Generator bridges this gap. It reads your SQL and reconstructs the structural picture. It focuses on Data Definition Language commands such as CREATE TABLE, ALTER TABLE, DROP TABLE, CREATE INDEX, and CREATE VIEW. It extracts table names, column types, primary keys, and foreign key relationships. The result is a diagram that mirrors what the database engine understands.

Many teams also want to adjust diagrams manually. Some relationships are logical rather than physical. Sometimes foreign keys are not declared but still exist in practice, for example in older systems. This tool supports both automatic detection and manual connection mode so you can complete the picture without editing the SQL first.

Key Features

• SQL editor with live parsing. The tool includes a full screen SQL editor where you can paste or type DDL statements. It counts characters, enforces a 100KB size limit, and uses a debounced parser so diagrams update a short time after you stop typing. This live feedback helps you refine schemas quickly.
• File upload for SQL scripts. You can upload .sql or .txt files directly. The tool reads them in the browser and validates their size before parsing. This is useful when you export DDL from existing databases or version controlled schema files.
• Support for key DDL commands. The parser understands CREATE TABLE with column definitions, inline and standalone primary key and foreign key constraints, ALTER TABLE with ADD, MODIFY, and DROP COLUMN, ADD CONSTRAINT PRIMARY KEY and FOREIGN KEY, DROP TABLE, CREATE INDEX, and CREATE VIEW (for table references). It pulls out the structure relevant to ER diagrams.
• Primary and foreign key detection. For each table, the tool builds a list of columns. It marks columns as primary keys when they appear in PK constraints or inline PRIMARY KEY definitions. It marks columns as foreign keys when inline or standalone REFERENCES clauses are present. It also records which table and column a foreign key points to.
• Automatic layout of table nodes. After parsing, the tool arranges tables into a grid layout. It computes an approximate number of columns based on the number of tables and positions each table node with spacing so diagrams are readable. This layout updates whenever you refresh or change the SQL.
• Interactive diagram canvas. The visual area uses a flow style canvas. Each table appears as a card with a colored header and a scrollable list of columns. You can pan and zoom, use a mini map to navigate, and adjust the view with built in controls. The background grid and colors help you see structure at a glance.
• Clear table node components. Each node shows the table name, column list, types, and PK/FK flags. Primary keys are marked with PK, foreign keys with FK. Types are shown in a small monospace badge. Long names wrap cleanly, and vertical scrolling in the node handles tables with many columns.
• Relationship edges with arrows. For each foreign key, the tool draws an edge from the referenced table to the referencing table. It uses distinct arrow markers and thicker colored lines. This lets you see child to parent relationships without reading the SQL.
• Manual connection mode. A connect button on the canvas toggles connection mode. When active, draggable handles appear on node edges. You can drag from the source handle of one table to the target handle of another to create custom connections. The tool prevents self connections and duplicate edges and shows clear errors if you try.
• Export to image and PDF formats. An export menu lets you download the current diagram as PNG, JPG, or WebP images or as a PDF. The tool uses a client side canvas capture and PDF generator. It hides controls and mini maps during capture and ensures nodes and labels stay visible and not clipped.
• AI powered schema generation. An AI assistant input lets you describe a database in plain language, such as “an e-commerce system with users, products, orders, and reviews.” The tool sends this description to a backend service which returns SQL DDL. The SQL is loaded into the editor and turned into a diagram.
• AI powered schema optimization. You can click an optimize button to ask the AI to refine your existing SQL. The backend returns improved DDL, which the tool loads into the editor and uses to update the diagram. This is optional and respects size limits so very large schemas are not sent.
• Sample schema loader. A sample button fills the editor with a realistic e-commerce schema including users, addresses, categories, products, orders, order_items, and reviews. It includes foreign keys, indexes, and ALTER statements. This sample is ideal for learning and quick demos.
• View mode controls. On desktop, you can switch between Editor only, Visual only, or Split view using buttons. On mobile, a small floating switch does the same. This allows you to focus on code, diagram, or both depending on your task and screen size.
• Download SQL for reuse. A download button saves the current SQL in the editor as a schema.sql file. This makes it easy to take AI generated or hand written schemas out of the tool and into your own projects.
• Error handling and status feedback. If parsing fails, input limits are hit, or export fails, the tool shows clear error banners at the top. It also shows progress states during AI operations and warns when character limits are close to being reached.

Common Use Cases

A backend developer inherits a legacy schema in a large .sql file. They upload the file into the ER Diagram Generator and immediately see a diagram of all tables and relationships. They use this to understand the system, identify key tables, and plan refactors.

A database designer working on a new product wants to explore different schema options. They describe possible designs to the AI assistant, get SQL proposals, and refine them. Each time they change the SQL, the diagram updates, helping them discuss trade offs with the team.

A technical writer preparing documentation for an internal system uses the tool to generate clean ER diagrams. They export diagrams as PNG or PDF and embed them into docs. The fact that diagrams come directly from real SQL reduces the risk of inconsistencies.

A teacher explaining database normalization uses the included sample schema as a base. They show how foreign key relationships create a normalized design for users, orders, and products. Students can read both the SQL and the visual diagram to understand concepts.

A DevOps engineer needs a quick view of database relationships before tuning performance. They paste recent DDL into the editor, see which tables are connected, and judge where indexes and partitioning might help. The diagram helps them avoid missing an important dependency.

A full stack developer who is more comfortable with visual tools uses the manual connection mode to express logical links that are not yet in SQL. This helps them communicate design ideas to the DBA before final constraints are added.

How to Use This Tool (Step-by-Step)

1. Open the ER Diagram Generator. You will see a two panel layout on larger screens: SQL Editor on the left and Visual diagram area on the right. On smaller screens you can switch between these views.
2. Decide how to provide your schema. To start from scratch, type or paste SQL DDL into the editor. To reuse existing scripts, click the upload icon and choose a .sql or .txt file. To experiment quickly, click the Sample button to load a prepared schema.
3. As you type or after upload, watch the character counter under the SQL Editor title. Keep your SQL under the configured size limit so parsing remains responsive.
4. When you stop typing for a short moment, the tool automatically parses your SQL. If it finds valid CREATE TABLE or ALTER TABLE statements, it extracts tables, columns, primary keys, and foreign keys. Any problems, such as no valid DDL found or parse errors, appear in an error banner.
5. Look at the Visual diagram area. If your schema is valid and contains tables, you will see each table as a card with its name and columns. Scroll and zoom to inspect the diagram. Use the mini map and controls to adjust your view.
6. Check that primary and foreign keys appear as expected. PK columns are marked, and FK columns show in tables that reference other tables. Relationship lines show how tables connect. If something is missing, return to the SQL Editor and adjust your DDL.
7. If you want to generate a schema from a description, go to the AI Assistant section under the editor. Type a short but clear description of your system and press the generate button. Wait while the backend returns SQL. The new SQL will replace the editor content and the diagram will update.
8. To refine an existing schema, click the Optimize Schema button. The tool sends your current SQL to the backend. If the AI returns an improved version, the editor and diagram update. Review changes before using them in production.
9. If you need to create or adjust relationships that are not in the SQL, enable Connect mode in the diagram panel. With connection mode on, drag from the source handle on one table to the target handle on another. The tool will create a new visual edge. If a connection already exists or you try to link a table to itself, you will see a clear message.
10. When you are ready to export the diagram, click the Export button in the canvas panel and choose your desired format: PNG, JPG, WebP, or PDF. The tool hides UI elements, captures the canvas, and downloads the result. Save it in your documentation or share with your team.
11. Use the view mode buttons at the bottom to choose Editor only, Split, or Visual only modes. Pick Split when you want to adjust SQL and see live changes, and Visual only when focusing on layout during presentations.
12. When you want to start over, click the Clear button in the editor toolbar. Confirm the action if you already have SQL. This will reset the editor, diagram, and any error messages.

Calculations & Logic

The ER Diagram Generator performs several structured parsing and layout steps. First, it cleans the SQL by removing single line comments and multi line comment blocks, while keeping line breaks. Then it splits the SQL into statements using semicolons followed by known keywords such as CREATE, ALTER, or DROP. Each statement is trimmed and processed.

For CREATE TABLE statements, it uses regular expressions to extract the table name and the inner column and constraint block. It splits this block by commas while tracking parenthesis depth to avoid breaking inside type definitions or function calls. Each part is then classified as a column definition, a standalone primary key constraint, or a foreign key constraint.

Column definitions record name, type, and whether they include inline primary key or references clauses. Standalone primary key constraints list columns that should be marked as PK. Standalone foreign key constraints list local and referenced columns and tables. After collecting all parts, the tool applies primary and foreign key labels to each column.

ALTER TABLE statements adjust existing tables or create placeholders when needed. The logic supports ADD COLUMN with optional PRIMARY KEY or REFERENCES info, MODIFY or ALTER COLUMN for type changes, ADD CONSTRAINT PRIMARY KEY and ADD CONSTRAINT FOREIGN KEY, and DROP COLUMN for removing columns. This lets the parser follow common schema evolution patterns.

DROP TABLE statements remove tables from the internal map. CREATE INDEX and CREATE VIEW statements record referenced tables so that diagram context includes resources even when full definitions are not present. Indexes do not add columns but help indicate that a table exists.

For layout, the tool counts tables and chooses a grid width based on the square root of the table count. Each table gets an x and y position based on its index. This simple layout aims for balanced diagrams without overlap. When you press Auto Layout, the tool recalculates positions based on the current SQL.

During export, the tool uses html2canvas to rasterize the React Flow container. Before capturing, it hides controls, minimap, and panels for a clean export. The capture logic validates that the canvas is not empty by checking pixel data in a small region. For PDF export, a PDF instance is created with dimensions that match the canvas, and the image is placed to fill the page. For image export, the canvas is converted to a blob and downloaded.

Reference Tables or Scales

Tips, Limitations & Best Practices

Keep your SQL input focused on DDL. Application level INSERT, UPDATE, or DELETE statements are not needed for ER diagrams and only add noise. When possible, paste or upload scripts with CREATE and ALTER commands only.

Remember that the parser focuses on structure, not every dialect detail. Very advanced or vendor specific features may not be fully recognized but should not break basic table and key detection. If something looks off, simplify the DDL or break it into smaller parts.

Use the sample schema to learn how foreign keys and indexes appear visually. Compare the SQL with the resulting diagram to build intuition, then apply the same patterns to your own schemas.

When using the AI features, start with small descriptions or schemas. This keeps responses fast and easier to review. Treat AI generated DDL as a proposal, not as final truth. Read and edit it before using it in your production database.

Before exporting diagrams, adjust zoom so that all important tables are visible and well spaced. The export function captures what is on screen, so a good viewport choice leads to better images and PDFs.

Use manual connection mode to highlight logical relationships that are not yet enforced by foreign key constraints. This is helpful when planning migrations where you intend to add constraints later.

Always keep a copy of your original SQL outside the tool. While the generator lets you edit and download SQL, your main schema should remain under version control in your own repositories.

Finally, remember that ER diagrams are a communication tool. Use clear table names and consistent column names, and update the diagram whenever the schema changes so the visual model stays in sync with the database.