Principle: Convention over configuration

Requiring explicit configuration for every aspect of a framework or library makes setup slow and error-prone. Users must learn and decide on many options before doing anything useful.

Provide sensible defaults that work out of the box, only require config for deviations:

Examples:

1. File-based routing (Next.js, Astro):

pages/about.tsx -> /about route (no router config needed)

1. Database table from model name:

class User -> users table (no explicit table name)

1. Test file discovery:

*.test.ts or __tests__/ (no test config listing each file)

1. Default ports:

Dev server on 3000, DB on 5432 (no config unless changed)

Principles for good defaults:

• 80% of users should never need to configure it
• Defaults should be safe and predictable
• Always allow overriding for the 20% who need it
• Document what the defaults are
• Don't change defaults in minor versions (breaking)

Anti-patterns:

• Requiring 50-line config file before 'hello world'
• Implicit behavior that can't be overridden
• Magic that varies by environment with no way to inspect it
• Defaults that are insecure (open ports, no auth)

Good defaults reduce cognitive load and time to productivity. They encode best practices so each user doesn't have to rediscover them.