How you can use Online Spell Checker for Japanese.
Copy and paste the required text into the form above, after that click the appropriate button. A pop-up window will appear showing your current text with errors highlighted in red and yellow. Click an error to get a list of correction suggestions. Choose the option that best fits your intended meaning to correct this mistake. If you added new text inside the window and you want to re-check it again, click "Check Text". After you're finished, click "Finish Checking"