Grammarly

Grammarly is the most widely used AI writing assistant in the world, with over 40 million daily users and integrations across 500,000+ apps and websites. What began as a grammar checker has evolved into a comprehensive writing AI covering tone, clarity, style, brand voice, plagiarism detection, and full document drafting.

Pricing: Free (basic grammar and spelling), Pro ($12/month billed annually, $30/month billed monthly, 1,000 AI prompt credits/month, advanced tone and style suggestions), Business ($14.50/user/month for teams of 10–49, $12.50/user for 50+, custom brand voice, team analytics, style guides). Enterprise pricing is custom.

Grammarly's key differentiator is ubiquity — it works inside Gmail, Google Docs, Notion, Slack, Word, LinkedIn, and thousands of other apps via browser extension, without switching context. GrammarlyGO provides prompt-based drafting, rewriting, and tone adjustment. For business teams, brand voice consistency features let organisations set their communication standards and have Grammarly enforce them across all employee writing.

The weaknesses are that the AI writing quality doesn't match dedicated tools like Claude or Jasper for long-form content, and the Pro plan's 1,000 AI prompt credits can run out for heavy users.