Cite:
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Responses
All API calls that change state will return a single element response (for XML calls).
They are formatted like this:
<?xml version="1.0" encoding="UTF-8"?>
<response success="false" reason="duplicate"/>

For JSON responses, they'll look like this:
{success: false, reason: "duplicate"}
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That's mean we can use API call to get data right?
https://konachan.com/post.json?limit=100&page=5&tags=%20rating:safe?api=my_api
I wanna get the json data but the response always 403 forbidden :(

You're not being very clear.

The first part of your post is a citation from the API documentation, though it's not clear why you included it. The link you posted is unrelated to the citation given that it doesn't change state. If you're having trouble with that link, it's because it's malformed (though it does appear to work fine in some browsers).

The "?api=my_api" part should be removed. First of all, you have two "?" in the url. If you wanted to add another property to the query string, you should use "&" instead of "?". Secondly, there is no "api" property. The API here doesn't use API keys.

Try:
https://konachan.com/post.json?limit=100&page=5&tags=rating:safe