Code to Flowchart: Visualize Your Logic Online

Why Code to Flowchart?

Reading code tells you what it does. Seeing a flowchart tells you how it works — the paths, decisions, and edge cases become instantly visible.

Real Example: Login Validation Function

Consider this JavaScript function that validates user login input:

function validateLogin(input) {
  const errors = [];

  if (!input.username || input.username.trim() === "") {
    errors.push("Username is required");
  } else if (input.username.length < 3) {
    errors.push("Username must be at least 3 characters");
  } else if (input.username.length > 20) {
    errors.push("Username must be at most 20 characters");
  }
  if (!input.password || input.password === "") {
    errors.push("Password is required");
  } else if (input.password.length < 8) {
    errors.push("Password must be at least 8 characters");
  }
  if (!input.email || input.email === "") {
    errors.push("Email is required");
  } else if (!input.email.includes("@")) {
    errors.push("Invalid email format");
  }
  return {
    valid: errors.length === 0,
    errors,
  };
}

How the Flowchart Visualizes This

When you paste this code into the Flowchart tool, it generates a Mermaid flowchart that shows the decision tree. Each if-else branch becomes a diamond decision node:

┌──────────────────┐
│   Start: Input   │
└──────┬───────────┘
       ▼
┌──────────────────┐
│  Username empty? │──Yes──→ "Username is required"
└──────┬───────────┘
       │ No
       ▼
┌──────────────────────┐
│  Username length < 3? │──Yes──→ "Min 3 characters"
└──────┬───────────────┘
       │ No
       ▼
┌───────────────────────┐
│  Username length > 20? │──Yes──→ "Max 20 characters"
└──────┬────────────────┘
       │ No
       ▼
┌──────────────────┐
│  Password empty?  │──Yes──→ "Password is required"
└──────┬───────────┘
       │ No
       ▼
┌────────────────────────┐
│  Password length < 8?   │──Yes──→ "Min 8 characters"
└──────┬─────────────────┘
       │ No
       ▼
┌──────────────────┐
│   Email empty?    │──Yes──→ "Email is required"
└──────┬───────────┘
       │ No
       ▼
┌─────────────────────┐
│  Email contains @?   │──No──→ "Invalid email format"
└──────┬──────────────┘
       │ Yes
       ▼
┌──────────────────────┐
│  Return { valid: true } │
└──────────────────────┘

Benefits of Visualizing This Flow

1. **Spot missing validations** — Looking at the chart, you might notice there's no check for whitespace-only passwords 2. **Optimize order** — The most common validation failures should come first for early exit 3. **Communicate with QA** — Hand the flowchart to your QA team; they can write test cases for every branch 4. **Document automatically** — The flowchart is always in sync with the code (unlike hand-drawn diagrams)

More Complex Example: Nested Decisions

For a nested decision structure like an order processing pipeline:

function processOrder(order) {
  if (!order.paymentComplete) {
    if (order.paymentMethod === "credit_card") {
      return retryPayment(order);
    }
    return "Awaiting payment";
  }
  if (!order.inventoryReserved) {
    return checkInventory(order);
  }
  if (!order.shippingLabel) {
    return generateLabel(order);
  }
  return dispatchOrder(order);
}

The flowchart immediately reveals the sequential pipeline structure and the branching at each validation gate.

Get Started

Use the Flowchart tool to instantly convert any JavaScript, Python, or pseudocode into a clear Mermaid flowchart. Paste code, see the visual structure, and understand your logic at a glance.