Example how to create a JSON from solidity

JSON.sol

function makeJSON() public view virtual returns (string memory) {

        return
            string(
                abi.encodePacked(
                    "data:application/json;base64,",
                    Base64.encode(
                        abi.encodePacked(
                            '{"name": "Bla #',
                            tokenId.toString(),
                            '", "description": "Description",',
                            '"image": "', _baseURI(), 'api/token/', tokenId.toString(), '.svg",'
                            '"external_url": "', _baseURI(), 'token/', tokenId.toString(), '",'
                            '"attributes": [{ "trait_type": "A", "value": "',
                            "1",
                            '"}, { "trait_type": "B", "value": "',
                            "2",
                            '"}, { "trait_type": "C", "value": "',
                            "3",
                            '"}, { "trait_type": "D", "value": "',
                            "4",
                            '"}, { "trait_type": "E", "value": "',
                            "5",
                            '"}, { "trait_type": "F", "value": "',
                            "6",
                            '"}]}'
                        )
                    )
                )
            );
    }