Spell check is, thankfully, something that smartphones support in this day and age. Grammar is a tougher nut to crack, though. On the desktop, Grammarly offers tools that go beyond a simple spell check, and now you can do that on Android, too. The new Grammarly Keyboard will pedantically pick apart everything you write in search of grammatical errors. However, it's a little lacking in actual keyboard features.
Grammarly Keyboard is easy to set up—just enable it and set the default like you would any other keyboard app. It looks similar to the Google Keyboard, but correction bubbles pop up at the top as you type. You can tap to accept the suggestion or tap the Grammarly button to see the errors expanded with explanations for the proposed change. It's not unlike Grammarly on the desktop.
You can log in with your Grammarly account, and premium users get advanced style suggestions. The free version isn't as powerful, but it does catch more than a regular spell check. The keyboard features are rather basic. There are no themes, swipe input, or layout options. Still, it's free if you want to see how your grammar stacks up.