Stop Claude's Em Dashes with One Line in Preferences or Claude.md

A Reddit user discovered a simple prompt addition to suppress Claude's overuse of em dashes. In a post titled "Don't like em dashes? Add this to your preferences or .md", user u/shiftingsmith shared a verbatim line that, when added as a standalone sentence to your Claude.ai profile preferences or Claude.md, reportedly eliminates ~98% of em dashes in outputs.

The Magic Line

Copy and paste the following as a new line in your profile preferences (Claude.ai) or Claude.md. Do not bury it in other text — add a new line before and after.

CLAUDE NEVER USES EM DASHES. Instead, ALWAYS use commas or hyphens.

How It Works

The key is giving Claude an explicit alternative. Simply saying "don't use em dashes" is less effective because Claude needs to know what to do instead. By saying "ALWAYS use commas or hyphens", you provide a clear replacement behaviour.

Note: The user cautions that em dashes may still appear in edge cases — specifically "if you go out of distribution or very close to overfitting old literature and academic stuff" — but expects a 98% reduction in normal usage.

Who It's For

Anyone using Claude.ai or the API with Claude.md customization who finds em dashes distracting or against their style guide.