---

name: converting-to-strong-types description: Converts loosely typed Bicep parameters using object or array to strongly typed alternatives like string[], user-defined types, or resource-derived types. Use when user mentions type safety, weak typing, object parameters, array parameters, resourceInput, resourceOutput, or asks to improve parameter definitions.

Converting to Strong Types

Replaces loose object and array parameter types with strong alternatives for compile-time validation and autocompletion.

Conversion Workflow

Copy and track progress:

Conversion Progress:
- [ ] Step 1: Identify loose types
- [ ] Step 2: Analyze parameter usage
- [ ] Step 3: Choose conversion strategy
- [ ] Step 4: Define types and update parameters
- [ ] Step 5: Validate with bicep build

Step 1: Identify loose types

Search for param <name> object and param <name> array declarations.

Step 2: Analyze parameter usage

Examine how the parameter is used in the template to determine expected structure.

Step 3: Choose conversion strategy

Pattern	Strategy
Array of primitives	string[], int[], bool[]
Array with constrained values	('value1' | 'value2')[]
Object matching resource property	resourceInput<'Type@Version'>.properties.X
Custom object structure	User-defined type with type keyword
Array of objects	User-defined type with [] suffix

Step 4: Define types and update parameters

Place type definitions above parameters. Add @description() decorators.

Step 5: Validate

Run bicep build <file> to verify syntax and type correctness.

Quick Reference

Simple Arrays

// Before
param addresses array

// After
param addresses string[]

Union Types (Constrained Values)

param environments ('dev' | 'staging' | 'prod')[]
param skuName 'Standard_LRS' | 'Premium_LRS'

User-Defined Types

type subnetType = {
  name: string
  addressPrefix: string
  nsgId: string?  // Optional property
}

param subnets subnetType[]

Resource-Derived Types

// Derive from Azure schema (Bicep 0.34.1+)
type accountKind = resourceInput<'Microsoft.Storage/storageAccounts@2024-01-01'>.kind
param storageProps resourceInput<'Microsoft.Storage/storageAccounts@2024-01-01'>.properties

For full resource-derived type details: See RESOURCE-DERIVED.md

Type Best Practices

• Use ? for optional properties: description: string?
• Use @sealed() to prevent extra properties at deployment
• Use @description() on types and properties
• Use constraints: @minLength(), @maxLength(), @minValue(), @maxValue()
• Compose complex types from simpler types

Common Patterns

For ready-to-use type definitions: See PATTERNS.md

Includes: tags, access policies, subnets, diagnostic settings, role assignments, private endpoints.

MCP Tools

Tool	Purpose
Bicep:get_bicep_best_practices	Current best practices
Bicep:get_az_resource_type_schema	Schema for resource-derived types
Bicep:list_az_resource_types_for_provider	Available types and API versions

Edge Cases

Dynamic objects (unknown keys): Use wildcard { *: string }

Mixed-type arrays: Use union (string | int | bool)[]

Backward compatibility: Use optional types ? for new properties