Rules help Firebender understand how to write high quality code. Add rules to the rules array in firebender.json to specify guidelines.

Rules apply to all features of Firebender such as autocomplete, chat, and inline AI changes

Firebender supports both project-specific rules and personal rules that apply across all projects. See Configuration Files for details on setting up personal rules.

To setup rules, you need to create a json file at the project root firebender.json.

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General Rules Example: Food delivery app

In $projectRoot/firebender.json:

firebender.json
{
  "rules": [
    "Project is a food delivery app (Doordash)",
    "Never use runBlocking",
    "Don't hardcode dpi",
    "Use `@SerializedName` for data/retrofit classes because code gets obfuscated",
    "Follow Material Design 3 guidelines and components",
    "Use Kotlin coroutines and Flow for asynchronous operations",
  ]
}

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Situational Rules Example: Test files

Here’s an example situational rule:

firebender.json
{
  "rules": [
    "Project is a food delivery app (Doordash)",
    {
      "filePathMatches": ["*Kotest.kt"],
      "rules": [
        "Use Kotest framework/BDD for tests"
      ]
    }
  ]
}

If you modify the file ProfileViewModelKotest.kt, AI will follow the rule Use Kotest framework/BDD for tests. If you modify MainActivity.kt, AI will not be provided the irrelevant rule.

filePathMatches follows the same regex notation as typical line in .gitignore.

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Full file rules

For complex or extensive rules, you can use external markdown files instead of embedding all rules in firebender.json. This solves several problems:

  • JSON has limitations for long strings
  • Projects often already have documentation (like README.md or ARCHITECTURE.md) that can be reused
  • Keeps rules organized and easier to maintain
firebender.json
{
  "rules": [
    "Use Kotlin for all new code",
    {
      "filePathMatches": "**/*.kt",
      "rulesPaths": "docs/architecture.md"
    }
  ]
}

With a corresponding docs/architecture.md file:

docs/architecture.md
# Android Architecture Guidelines

## UI Layer
- Use Jetpack Compose for new UI components
- Follow Material Design 3 guidelines
- Implement unidirectional data flow with ViewModels

## Data Layer
- Use Room for local database storage
- Implement Repository pattern for data access
- Use Retrofit for network operations

Firebender will include both inline rules and rules from the referenced external files when processing matching files.

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Reading Errors

Rules will use the latest file saved immediately. If there are parsing errors it will tell you which fields were incorrect:

In this case, rules[0].filePathMatches is supposed to be a string and not an array.

For a complete reference of the rules syntax including advanced patterns and configuration options, see the Rules Syntax Documentation.