Go Template Syntax Guide

Updated Jan 7, 2026
DataMagik Documents

The DataMagik Document Designer uses Go's powerful template syntax for dynamic content generation. This guide covers the fundamentals with extensive examples.

Table of Contents

  • Basic Variable Substitution
  • Nested Object Access
  • Array Access
  • Comments
  • Whitespace Control
  • Pipeline Operations
  • Variables in Templates

Basic Variable Substitution

Simple Variables

Access data fields using dot notation with double curly braces:

<h1>{{.Title}}</h1>
<p>{{.Description}}</p>
<span>{{.Amount}}</span>

Sample Data:

{  
  "Title": "Monthly Report",  
  "Description": "Sales performance for September",  
  "Amount": 12500.50
}

Output:

<h1>Monthly Report</h1>
<p>Sales performance for September</p>
<span>12500.50</span>

Multiple Variables in One Line

<p>Hello {{.FirstName}} {{.LastName}}, your balance is ${{.Balance}}</p>

Sample Data:

{  
  "FirstName": "John",  
  "LastName": "Doe",  
  "Balance": 1250.75
}

Output:

<p>Hello John Doe, your balance is $1250.75</p>

Nested Object Access

Accessing Nested Properties

Use dot notation to access nested object properties:

<h2>{{.Customer.Name}}</h2>
<p>Email: {{.Customer.Email}}</p>
<p>{{.Customer.Address.Street}}</p>
<p>{{.Customer.Address.City}}, {{.Customer.Address.State}} {{.Customer.Address.Zip}}</p>

Sample Data:

{  
  "Customer": {    
    "Name": "Acme Corporation",    
    "Email": "contact@acme.com",    
    "Address": {      
      "Street": "123 Business Ave",      
      "City": "New York",      
      "State": "NY",      
      "Zip": "10001"    
      }  
    }
}

Output:

<h2>Acme Corporation</h2>
<p>Email: contact@acme.com</p>
<p>123 Business Ave</p>
<p>New York, NY 10001</p>

Deep Nesting Example

<div class="order">  
<h3>Order {{.Order.Number}}</h3>  
<p>Shipped to: {{.Order.Shipping.Recipient.Name}}</p>  
<p>{{.Order.Shipping.Recipient.Address.Line1}}</p>  
<p>Tracking: {{.Order.Shipping.TrackingNumber}}</p>
</div>

Sample Data:

{  
  "Order": {    
    "Number": "ORD-2025-001",    
    "Shipping": {      
      "Recipient": {        
      "Name": "Jane Smith",        
      "Address": {          
        "Line1": "456 Oak Street"        
        }      
      },      
    "TrackingNumber": "1Z999AA10123456784"    
    }  
  }
 }

Array Access

Direct Index Access

Access array elements by index:

<p>First item: {{index .Items 0}}</p>
<p>Second item: {{index .Items 1}}</p>
<p>Third item: {{index .Items 2}}</p>

Sample Data:

{  "Items": ["Apple", "Banana", "Cherry"]}

Output:

<p>First item: Apple</p>
<p>Second item: Banana</p>
<p>Third item: Cherry</p>

Accessing Array of Objects

<p>First customer: {{(index .Customers 0).Name}}</p>
<p>First customer email: {{(index .Customers 0).Email}}</p>

Sample Data:

{  
  "Customers": [    
    {
      "Name": "Alice Johnson",      
      "Email": "alice@example.com"    
    },    
    {
      "Name": "Bob Wilson",      
      "Email": "bob@example.com"    
    }  
  ]
}

Output:

<p>First customer: Alice Johnson</p>
<p>First customer email: alice@example.com</p>

Comments

Single-Line Comments

Comments are not rendered in the output:

{{/* This is a comment and won't appear in output */}}
<p>{{.Message}}</p>
{{/* Another comment */}}

Multi-Line Comments

{{/*  This is a multi-line comment  It can span multiple lines  and won't appear in the output*/}}
<div>{{.Content}}</div>

Documentation Comments

Use comments to document your template:

{{/* Customer Information Section */}}
<div class="customer-info">  
{{/* Display customer name and ID */}}  
<h2>{{.Customer.Name}} (ID: {{.Customer.ID}})</h2>    
{{/* Contact details */}}  
<p>Email: {{.Customer.Email}}</p>  
<p>Phone: {{.Customer.Phone}}</p>
</div>

Whitespace Control

Default Behavior

By default, whitespace around template tags is preserved:

<p>  {{.Name}}</p>

Output includes newlines and spaces.

Trim Whitespace Before

Use {{- to remove whitespace before the tag:

<p>  {{- .Name}}</p>

Trim Whitespace After

Use -}} to remove whitespace after the tag:

<p>  {{.Name -}}</p>

Trim Both Sides

Combine both for complete whitespace control:

<ul>  
    {{- range .Items}}  
    <li>{{- .Name -}}</li>  
    {{- end}}
</ul>

Sample Data:

{  
  "Items": [    
    {"Name": "Item 1"},    
    {"Name": "Item 2"},    
    {"Name": "Item 3"}  
  ]
}

Output (compact):

<ul><li>Item 1</li><li>Item 2</li><li>Item 3</li></ul>

Pipeline Operations

Using Pipes

Chain operations using the pipe operator |:

<p>{{.Name | upper}}</p><p>{{.Description | lower}}</p><p>{{.Title | title}}</p>

Sample Data:

{  "Name": "john doe",  "Description": "IMPORTANT MESSAGE",  "Title": "hello world"}

Output:

<p>JOHN DOE</p>
<p>important message</p>
<p>Hello World</p>

Multiple Pipe Operations

Chain multiple operations:

<p>{{.Email | lower | printf "Contact: %s"}}</p>

Pipe with Function Arguments

<p>{{.Price | printf "%.2f"}}</p>
<p>{{.Date | dateFormat "January 2, 2006"}}</p>

Sample Data:

{  
  "Price": 1234.5,  
  "Date": "2025-09-21"
}

Output:

<p>1234.50</p>
<p>September 21, 2025</p>

Variables in Templates

Declaring Variables

Use $variable := value syntax to create template variables:

{{$total := .Amount}}
<p>Amount: ${{$total}}</p>
<p>With Tax: ${{$total | printf "%.2f"}}</p>

Variables in Loops

Capture loop values in variables:

{{range $index, $item := .Products}}
  <div>    
    <p>{{$index}}. {{$item.Name}}</p>    
    <p>Price: ${{$item.Price}}</p>  
  </div>
{{end}}

Sample Data:

{  
  "Products": [    
    {
      "Name": "Widget", 
      "Price": 19.99},    
    {
      "Name": "Gadget", 
      "Price": 29.99},    
    {
      "Name": "Doohickey", 
      "Price": 39.99
    }  
  ]
}

Output:

<div>  
  <p>0. Widget</p>  
  <p>Price: $19.99</p>
</div>
<div>  
  <p>1. Gadget</p>  
  <p>Price: $29.99</p>
</div>
<div>  
  <p>2. Doohickey</p>  
  <p>Price: $39.99</p>
</div>

Using Variables for Calculations

{{$subtotal := .Subtotal}}
{{$taxRate := .TaxRate}}
{{$tax := .Tax}}
{{$total := .Total}}
<table>  
  <tr><td>Subtotal:</td><td>${{$subtotal}}</td></tr>  
  <tr><td>Tax Rate:</td><td>{{$taxRate}}%</td></tr>  
  <tr><td>Tax:</td><td>${{$tax}}</td></tr>  
  <tr><td>Total:</td><td>${{$total}}</td></tr>
</table>

Capturing Context

Save the current context for later use:

{{$root := .}}
{{range .Orders}}  
  <div>    
    <p>Order: {{.Number}}</p>    
    <p>Company: {{$root.CompanyName}}</p>  \
  </div>
{{end}}

Sample Data:

{  
  "CompanyName": "Acme Corp",  
  "Orders": [    
    {
      "Number": "ORD-001"
    },    
    {
      "Number": "ORD-002"
    }  
  ]
}

Output:

<div>  
  <p>Order: ORD-001</p>  
  <p>Company: Acme Corp</p>
</div>
<div>  
  <p>Order: ORD-002</p>  
  <p>Company: Acme Corp</p>
</div>

Complete Example: Invoice Template

Here's a comprehensive example combining multiple concepts:

<!DOCTYPE html>
<html>
<head>  
	<title>Invoice {{.InvoiceNumber}}</title>  
    <style>    
      body { font-family: Arial, sans-serif; }    
      .header { border-bottom: 2px solid #333; padding-bottom: 20px; }    
      .item { border-bottom: 1px solid #ddd; padding: 10px 0; }    
      .total { font-weight: bold; font-size: 1.2em; }  
    </style>
</head>
<body>  
  {{/* Invoice Header */}}  
<div class="header">    
  <h1>{{.Company.Name | upper}}</h1>    
  <p>{{.Company.Address.Street}}</p>    
  <p>{{.Company.Address.City}}, {{.Company.Address.State}} {{.Company.Address.Zip}}</p>  
</div>  
{{/* Invoice Details */}}  
<div class="details">    
  <h2>Invoice #{{.InvoiceNumber}}</h2>    
  <p>Date: {{.InvoiceDate | dateFormat "January 2, 2006"}}</p>    
  <p>Due: {{.DueDate | dateFormat "January 2, 2006"}}</p>  
</div>  
{{/* Customer Information */}}  
<div class="customer">    
  <h3>Bill To:</h3>    
    <p>{{.Customer.Name}}</p>    
    <p>{{.Customer.Email}}</p>  
</div>  
{{/* Line Items */}}  
<table>    
  <thead>      
    <tr>        
      <th>Description</th>        
      <th>Qty</th>        
      <th>Price</th>        
      <th>Total</th>      
    </tr>    
  </thead>    
  <tbody>      
  {{- range .Items}}      
  <tr class="item">        
    <td>{{.Description}}</td>        
    <td>{{.Quantity}}</td>        
    <td>${{.Price | printf "%.2f"}}</td>        
    <td>${{.Total | printf "%.2f"}}</td>      
  </tr>      
  {{- end}}    
  </tbody>  
  </table>  
  {{/* Total */}}  
  <div class="total">    
    <p>Subtotal: ${{.Subtotal | printf "%.2f"}}</p>    
    <p>Tax ({{.TaxRate}}%): ${{.Tax | printf "%.2f"}}</p>    
    <p>Total: ${{.TotalAmount | printf "%.2f"}}</p>  
  </div>
</body>
</html>

Sample Data:

{  
  "Company": {    
    "Name": "My Company Inc.",    
    "Address": {      
      "Street": "123 Main Street",      
      "City": "Anytown",      
      "State": "CA",      
      "Zip": "90210"    
    }  
  },  
  "InvoiceNumber": "INV-2025-001",  
  "InvoiceDate": "2025-09-21",  
  "DueDate": "2025-10-21",  
  "Customer": {    
    "Name": "Acme Corporation",    
    "Email": "billing@acme.com"  
  },  
  "Items": [    
    {      
      "Description": "Web Development Services",      
      "Quantity": 40,      
      "Price": 125.00,      
      "Total": 5000.00    
    },    
    {      
      "Description": "Design Services",      
      "Quantity": 20,      
      "Price": 100.00,      
      "Total": 2000.00    
    }  
  ],  
  "Subtotal": 7000.00,  
  "TaxRate": 8.5,  
  "Tax": 595.00,  
  "TotalAmount": 7595.00
}

Next Steps

  • Learn about String Functions for text manipulation
  • Explore Date & Time Functions for date formatting
  • Master Control Flow for conditional logic and loops

Related Documentation:

Go Template Package - Official Go documentation

Previous DataMagik Documents Next String Functions Guide
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