I am using Form Data format for APIs. The thing is how I am going to make OpenAPI input being larger by using textarea? Answer i’ve hacked. my way is when specific field name, change input(type=text) to textarea. first, you serve self-hosting javascript and css for docs. https://fastapi.tiangolo.com/advanced/extending-openapi/#self-hosting-javascript-and-css-for-docs. second, you change javascript source code like this. you can hack css