How do I support templates and variables in notification messages?

A good way to support templates and variables in notification messages is to separate:

1. the message definition
2. the data used to fill it in at send time

1) Use a template format

Store message text with placeholders, for example:

• "Hello {{name}}, your order {{orderId}} has shipped."
• "Hi {name}, your balance is {balance}."

Common choices:

• Mustache / Handlebars-style: {{name}}
• Python-style: {name}
• Liquid: {{ customer.name }}

Pick one and use it consistently.

2) Pass variables when sending

When sending a notification, provide a variables object/map:

{
  "template": "Hello {{name}}, your order {{orderId}} has shipped.",
  "variables": {
    "name": "Ada",
    "orderId": "12345"
  }
}

Rendered output:

Hello Ada, your order 12345 has shipped.

3) Render server-side

Usually best to render the template on the backend before dispatching the notification. Benefits:

• consistent output
• easier validation
• safer than letting clients render arbitrary templates
• simpler auditing/logging

4) Support defaults and missing values

Decide what happens if a variable is missing:

• fail the send
• leave placeholder unchanged
• substitute a default value

Example:

• {{name | default:"there"}}

5) Keep templates editable but controlled

If non-developers will edit notification text:

• store templates in a database or CMS
• expose a template editor with preview
• restrict allowed variables per template

Example metadata:

{
  "id": "order_shipped",
  "body": "Hello {{name}}, your order {{orderId}} has shipped.",
  "allowedVariables": ["name", "orderId"]
}

6) Validate variables

Before rendering:

• ensure required variables are present
• ensure types are correct
• sanitize any user-provided content if needed

7) Preview before sending

A preview endpoint helps:

{
  "templateId": "order_shipped",
  "variables": {
    "name": "Ada",
    "orderId": "12345"
  }
}

Return the rendered message so users can confirm it.

8) Example implementation idea

Template

Hi {{firstName}}, your verification code is {{code}}.

Send data

{
  "firstName": "Maya",
  "code": "839201"
}

Rendered

Hi Maya, your verification code is 839201.

9) If you need advanced logic

If you need conditionals, loops, or localization, choose a richer templating engine:

• Handlebars
• Liquid
• Jinja2 (Python)
• EJS (JavaScript)

Example conditional:

Hello {{name}}{{#if premium}}, thanks for being a premium member{{/if}}.

If you want, I can also show:

• a database schema for templated notifications
• a Node.js / Python / Java example
• or a recommended API design for sending templated messages