Hi Yaco

There are a couple of ways of achieving this

You could create an Alternate Template for the BlogPost and if DisableAlternativeTemplates is set to false in AppSettings, it means you can request any url of the site, and force it to use the alternative template instead of the selected template

So if you had a url:

https://www.mylovelysite/blogs/ten-exciting-things-you-wont-believe

as a blog post, you could request that blog post via the alternative template using it's alias eg

https://www.mylovelysite/blogs/ten-exciting-things-you-wont-believe?altTemplate=jsonOnly

(so your template would have alias 'jsonOnly'...

If you enabled the old 'ContentFinderByUrlAndTemplate' ContentFinder - https://github.com/umbraco/Umbraco-CMS/blob/e0d9084d04d667fda38908025eb181577ca7fa34/src/Umbraco.Core/DependencyInjection/UmbracoBuilder.Collections.cs#L58

then this would also be routable via the Url

https://www.mylovelysite/blogs/ten-exciting-things-you-wont-believe/jsonOnly

you'd then need to implement the template (you can route hijack with an alias matching the alt template) to render the JSON version of the blog post.

OR

You could create your own API Endpoint, and route it how you prefer by implementing an UmbracoApiController:

plenty of examples here:

https://docs.umbraco.com/umbraco-cms/reference/routing/umbraco-api-controllers/

That would give you full control over the request and what is returned.

OR

In Umbraco 12 there is this Content Delivery API everyone is going on about.... https://www.youtube.com/watch?v=CYdwW4DtK3o

regards

Marc