---
title: Flags (named options)
description: Parameters without [Argument] become --kebab-case long flags. A bool flag defaults to false; pass --flag to set it. C# parameter names are automatically...
url: https://docs-v3-preview.elastic.dev/argh/parameters/flags
---

# Flags (named options)
Parameters without `[Argument]` become `--kebab-case` long flags. A `bool` flag defaults to `false`; pass `--flag` to set it.
```csharp
public static Task<int> Build(string outputDir, bool release = false) { … }
// myapp build --output-dir ./bin --release
```


## Naming convention

C# parameter names are automatically converted from camelCase to kebab-case:
- `outputDir` → `--output-dir`
- `dryRun` → `--dry-run`
- `verbose` → `--verbose`


## Long name override

By default the CLI long name is derived from the C# parameter name. To use a different primary name, place a `--long-name` token before the description in an XML `<param>` tag.
Additional `--names` after the first become aliases. Once an explicit long name is specified, the derived name is dropped entirely.
```csharp
/// <summary>Tag one or more resources.</summary>
/// <param name="tags">-t, --tag, Tags to apply.</param>
public static void Tag(string[] tags) { … }
```

```
--tag a --tag b    ✓  (explicit primary name)
-t a               ✓  (short alias)
--tags             ✗  (derived name is dropped)
```

```csharp
/// <param name="outputDir">-o, --out, --output, Output directory.</param>
public static void Build(string outputDir) { … }
```

```
--out ./bin         ✓  (primary)
--output ./bin      ✓  (alias)
-o ./bin            ✓  (short alias)
--output-dir        ✗  (derived name is dropped)
```

<tip>
  This also works on `[AsParameters]` properties, fields, and primary-constructor parameters via their `<summary>` or `<param>` doc lines.
</tip>


## Nullable bool - `--flag` / `--no-flag` pairs

A `bool?` flag generates **both** `--flag` (sets `true`) and `--no-flag` (sets `false`). Omitting either leaves the value `null`, letting you distinguish "not specified" from an explicit false.
Help output shows `--flag / --no-flag` for nullable bools.
```csharp
public static Task<int> Deploy(string env, bool? dryRun = null) { … }
// myapp deploy staging               → dryRun is null
// myapp deploy staging --dry-run     → dryRun is true
// myapp deploy staging --no-dry-run  → dryRun is false
```


## Required vs optional

Parameters without a default value are required flags. Parameters with a default value are optional.
```csharp
public static Task<int> Deploy(
    string environment,          
    bool dryRun = false,         
    string? region = null)       
{ … }
```


## Collections

Collection flags (`T[]`, `List<T>`) accept the flag multiple times by default. Use `[CollectionSyntax]` for comma-separated values instead.
```csharp
public static Task<int> Deploy(string[] targets, [CollectionSyntax(Separator = ",")] string[] tags) { … }
// Repeated:   myapp deploy --targets web --targets api
// Separator:  myapp deploy --targets web,api --tags blue,green
```