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Diagram Generator — Free Online Diagram Generator | Thefreeaitools

Diagram Generator

Create UML diagrams, flowcharts, org charts, mind maps, Merise MCD and MLD models, Mermaid diagrams, and data charts, then export them as PNG, SVG, or PDF — all in your browser, with no sign-up.

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Last updated: August 24, 2026

How to Use the Diagram Generator

  1. Choose a diagram type from the Diagram type selector: Class, Use Case, Sequence, Activity, State Machine, Component, Deployment, ERD, Flowchart, Organization Chart, or Mind Map. The editor immediately loads a complete sample for that type so you can see the syntax in action.
  2. Describe your model in the Diagram source text area. Every node starts with a short tag (@c for a class, @a for an actor, @p for a process step, @entity for a database entity), and connectors such as --, -->, *--, and ..> join named nodes. The canvas redraws itself about 300 milliseconds after you stop typing.
  3. Adjust the layout from the controls row: flow direction (left-to-right or top-to-bottom), orthogonal or direct connectors, curved edges, and three themes (black and white, blueprint, sketch). The Switch direction button flips the flow instantly.
  4. Click any node or edge on the canvas to select it, then use Duplicate or Delete. Double-clicking a node moves the cursor to its line in the editor. Undo and Redo (or Ctrl+Z and Ctrl+Y) walk through every change.
  5. Rearrange the drawing directly on the canvas: drag any shape to move it — the connectors follow and re-route around the other shapes, and dragging a system boundary moves its whole group. Moved shapes stay where you put them as you keep editing, and Reset positions returns everything to the automatic layout.
  6. Rename anything right on the canvas: double-click a node to edit its text (Enter confirms, Escape cancels), double-click an edge to change its label, and double-click empty space to drop a new node exactly there and name it immediately. Select a node and press the arrow keys to nudge it, or hold Ctrl while scrolling to zoom the preview.
  7. For charts, open the Charts tab, pick one of the ten types (bar, line, area, pie, donut, radar, scatter, bubble, gauge, funnel), and keep your data as comma-separated rows with a header line. Click Apply, and every numeric cell is validated — if something is wrong you get the exact row and column, not a blank screen.
  8. Export with the buttons above each canvas: PNG (high resolution, white background), SVG (vector, editable in Inkscape or Illustrator), and PDF (A4, automatic orientation). Diagram models also export as Mermaid code, draw.io XML, or JSON, and the Merise MLD copies or downloads as plain text.

Why Use Our Diagram Generator?

Our diagram generator turns plain text into professional UML diagrams, flowcharts, entity-relationship models, and charts in under a second. Because every model is described with a compact text syntax, you can draft a six-table ERD in the time it takes a drag-and-drop tool to open. There is no canvas grid to fight: the built-in layout engine measures every shape, computes a layered arrangement, and routes orthogonal or curved connectors around your nodes, so even a 40-node diagram stays readable without manual nudging.

As a UML diagram maker it covers the notation that actually ships software: class compartments with attributes and methods, use case ellipses inside system boundaries, sequence lifelines with synchronous and asynchronous messages, activity and state machine flows, and component or deployment views. Multiplicities, aggregation, composition, inheritance, dependency, and realization all render with standard arrowheads and labels, and the same model exports to Mermaid and draw.io so it round-trips into your documentation pipeline.

As an online chart maker it treats your CSV rows as the single source of truth. Bar charts support grouped and stacked series in vertical or horizontal orientation; line and area charts join points with crisp polylines; pie and donut charts show values and percentages; radar, scatter, bubble, gauge, and funnel types cover reports that ordinary spreadsheet exports miss. The Merise MCD generator goes one step further: it validates cardinalities and derives the relational MLD with foreign keys and association tables, which is exactly the transformation taught in French-speaking database courses.

Nothing here requires an account, an installation, or an internet connection after the page loads. The whole engine — parser, layout, renderer, and exporters — runs in JavaScript inside your browser, so diagrams of internal systems, confidential databases, or unreleased products never touch a server. That combination of speed, breadth, and privacy is why teams keep a tab with this tool open during design meetings.

Worked example: ERD for an order system

Paste this exact source into the Diagrams tab with the ERD type selected:

@entity Client
idClient INT PK
nom VARCHAR
email VARCHAR

@entity Commande
numCommande INT PK
dateCommande DATE

@entity Produit
refProduit INT PK
designation VARCHAR

@entity LigneCommande
quantite INT

Client 1--N Commande : passer
Commande 1--N LigneCommande : contenir
Produit 1--N LigneCommande : concerner

The generator renders four entity boxes with their attributes listed under a double header rule, primary keys underlined in every box, and three connectors labeled passer, contenir, and concerner with a blue 1 at each parent end and a blue N at each child end. Switching the flow to Top to bottom restacks the same model vertically in one click, and the JSON export returns the full model with node ids, attribute lists, and edge multiplicities so a later session can rebuild it exactly.

Common Mistakes to Avoid

  • Writing multiplicities as 1.* or 1-n. The parser reads the standard UML forms — 1..*, 0..1, *, N — so write Order "1" *-- "1..*" OrderItem : contains and not 1.*.
  • Putting the Merise cardinality on the wrong side. In Client 1,1 -- 0,N Commande, the (1,1) next to Client means one Commande belongs to exactly one Client; if you write it the other way around, the derived MLD places the foreign key in the wrong table.
  • Expecting the tool to keep draw.io coordinates. Imported .drawio files keep every node, connector, and label, but the layout is recalculated with the built-in engine — that is what keeps imported models tidy instead of faithfully importing a mess.
  • Giving chart series a text header without numeric rows. A header line like Month,Revenue is fine, but if a value cell contains text, the validator reports its exact row and column before anything renders.

Privacy and Security

Every diagram, chart, dataset, and export is processed entirely in your browser. The parsers, the layout engine, the SVG renderer, and the PNG and PDF exporters are plain JavaScript running on your device, so no diagram text, no CSV row, and no Mermaid source is ever sent to a server, and nothing is stored, logged, or shared after you close the tab.

The page is served over HTTPS from Thefreeaitools.com, which protects the transfer of the tool itself; once loaded, the generator even keeps working offline. Because files you import are read with the browser's local file APIs and files you export are assembled as Blob downloads, sensitive models of internal systems never appear in any server log or analytics report.