7 Best AI Tools for Writing a Book in 2026 (Fiction and Non-Fiction)
Short answer: use Sudowrite if you're writing fiction, Claude if you're writing non-fiction, and Novelcrafter if you want the most control over how AI fits into your writing process.
The self-publishing market hit $4.2 billion in 2025, and surveys show that around 30% of indie authors now use AI somewhere in their writing workflow. Not to generate entire books (Amazon KDP requires you to disclose AI-generated content, and readers can smell fully AI-written prose from a paragraph away). The real use case is using AI to break through writer's block, draft scenes you'll rewrite, outline chapters, brainstorm plot alternatives, and edit faster. The tools that understand this distinction are the ones worth paying for.
I've tested every major option for both fiction and non-fiction projects. Here's what actually works.
Quick comparison
| Tool | Best for | Price | Standout feature |
|---|---|---|---|
| Sudowrite | Fiction writing | $19-69/mo | Story Engine, voice matching |
| Claude | Non-fiction, long-form | Free/$20/mo | 200K context, best prose quality |
| Novelcrafter | Outlining + drafting | $9-25/mo | Codex system, multi-model |
| ChatGPT | Brainstorming, outlines | Free/$20/mo | Custom GPTs for writing |
| Squibler | Full book generation | $18-38/mo | End-to-end book workflow |
| ProWritingAid | Self-editing | $10-15/mo | 25+ writing reports |
| Plottr | Outlining | $25/yr-$199 lifetime | Visual timeline plotting |
Sudowrite
Sudowrite is built specifically for fiction. Not marketing copy, not blog posts, not emails. Fiction. And that specialization shows in features that general-purpose AI tools don't offer.
Story Engine is the headline feature. You feed it your outline, character descriptions, style preferences, and a few sample paragraphs of your writing voice. Then it generates draft chapters that actually sound like you, not like a corporate AI. I gave it three pages of first-person noir and the output maintained the short sentences, cynical observations, and understated descriptions. It lost some rhythm on longer passages, but the bones were right.
Other key features:
- Describe: expands a bare sentence into sensory-rich prose ("She walked into the bar" becomes a paragraph with lighting, sounds, smells, atmosphere)
- Brainstorm: generates plot alternatives when you're stuck
- Rewrite: offers variations on a passage in different tones
These aren't gimmicks. They solve the specific problems fiction writers face at 2 AM when the deadline is tomorrow.
Hobby & Student at $19/month (225 AI credits, ~30,000 words). Professional at $29/month (1,000 credits). Max at $69/month (3,400 credits).
Most novelists on the Professional plan report it lasting through a full month of active writing.
Ratings: Capterra: 4.5/5. Trustpilot: 4.3/5.
The limitation: Sudowrite isn't a general writing tool. Don't use it for your non-fiction business book or memoir (unless the memoir reads like a novel). And the AI-generated prose always needs your editing pass. It's a first-draft accelerator, not a replacement for your voice.
Claude
Claude is my top pick for non-fiction books, and the reason is simple: the 200K token context window. That's roughly 150,000 words, or about two full-length books. You can paste an entire manuscript into a single conversation and ask Claude to analyze structure, identify gaps, check consistency, or rewrite specific chapters while maintaining awareness of everything else.
No other AI tool handles long-form context this well. ChatGPT cuts off at much shorter context lengths in practice (even though the window is technically large, quality degrades). Claude maintains coherent reasoning across the full window.
For a 60,000-word non-fiction book, I pasted the complete draft and asked Claude to identify every instance where I made a claim without supporting evidence. It found 23 spots I'd missed in three editing passes.
The prose quality is noticeably better than ChatGPT for book-length writing. Claude's output reads more naturally, avoids repetitive sentence structures, and handles nuance better. You can also use Claude through the AI Academy to learn workflows for integrating it into your writing process.
Free tier (limited daily usage). Pro at $20/month. Max at $100/month (5x capacity).
Where Claude falls short: it won't maintain your writing voice as faithfully as Sudowrite for fiction. No built-in story structure tools, character databases, or timeline features. It's a brilliant writing partner in a blank chat window, not a purpose-built book writing application.
Novelcrafter
Novelcrafter gives you something no other tool does: a structured knowledge base called a Codex that the AI references while helping you write. You build entries for characters, locations, magic systems, historical facts, timeline events, and anything else relevant. When you ask the AI to draft a scene, it pulls from your Codex to maintain consistency.
That Codex system solves the biggest problem with using AI for books: context loss. ChatGPT forgets your character's eye color three prompts later. Novelcrafter's AI always knows that Marcus has a scar above his left eyebrow and grew up in Birmingham because that's in the Codex entry you wrote.
The platform supports multiple AI models (GPT-5.2, Claude, and others), and you bring your own API keys for some models. Use Claude for complex plotting, GPT for quick dialogue generation, and a cheaper model for brainstorming throwaway ideas.
Hobbyist at $9/month (core features, limited AI). Crafter at $15/month (full Codex, enhanced AI). Wordsmith at $25/month (everything, priority generation).
Kindlepreneur rated it the most powerful AI tool for writers. The learning curve is steeper than Sudowrite since you need to build out your Codex first, but that upfront investment pays off across a full novel.
ChatGPT
ChatGPT isn't purpose-built for books, but it's the most versatile brainstorming partner available. The combination of GPT-5.2's reasoning quality and Custom GPTs makes it surprisingly useful.
Custom GPTs are where the value lives for authors:
- GPTs trained for plotting using three-act structure, Save the Cat beat sheet, Hero's Journey
- Character development questionnaires and world-building checklists
- Dialogue coaching and genre-specific writing assistants
- Build your own Custom GPT with your book's bible and style guide uploaded as knowledge
For brainstorming, nothing beats typing "give me 10 ways this heist could go wrong" and getting usable ideas in seconds. I use ChatGPT for the messy early stages: outlining chapters, generating character backstories, stress-testing plot logic, and asking "what's the weakest part of this chapter?"
Free tier for occasional brainstorming. Plus at $20/month for GPT-5.2 access. See our guide to using AI to write a book for specific prompt strategies.
The downside: ChatGPT loses context in long conversations. After 20-30 exchanges about your novel, it starts contradicting earlier decisions. You need to re-paste key information or start new conversations for different aspects of your book.
Squibler
Squibler positions itself as the all-in-one AI book writing platform. Upload your idea, and Squibler generates an outline, writes chapter drafts, and lets you iterate through the full manuscript in a single interface.
The AI generates full chapter drafts of 3,000-5,000 words each. A "book generation" feature can produce a rough draft of an entire book in hours. Quality varies: some chapters need light editing, others require near-complete rewrites. But as a starting point to react against rather than a blank page, it moves faster than any other tool here.
Standard at $18/month. Premium at $38/month (unlimited generation, all features).
Ratings: G2: 4.3/5.
The trade-off is quality versus speed. Squibler prioritizes getting words on the page fast. If you're publishing a high-quality literary novel, the output needs substantial editing. If you're producing non-fiction guides, course materials, or genre fiction where speed matters more than prose artistry, Squibler makes practical sense.
ProWritingAid
ProWritingAid isn't an AI writing tool. It's an AI editing tool, and that distinction matters. Once you have a draft, ProWritingAid analyzes it across 25+ dimensions:
- Readability and sentence structure
- Dialogue tags ("he exclaimed," "she whispered angrily")
- Pacing: visualizes slow and fast sections across your manuscript
- Echoes: catches repeated words and phrases within proximity
- Cliches, passive voice, transitions, and more
These are the problems a good developmental editor would flag, available instantly and repeatedly as you revise.
Monthly at $30/month. Yearly at $120/year ($10/month). Lifetime at $399 one-time, exceptional value for anyone planning to write more than one book.
Ratings: G2: 4.5/5 (480+ reviews). Trustpilot: 4.4/5. Integrates with Scrivener, Google Docs, Word, and most browser-based writing tools.
Plottr
Plottr is a plotting and outlining tool with visual timeline and beat sheet features. If you're the kind of writer who needs to see your entire story structure mapped out before writing, Plottr turns that mental model into an interactive visual board.
Key features:
- Timeline rows for each character or subplot with draggable scene cards
- Built-in templates: three-act structure, Save the Cat, Hero's Journey, Romancing the Beat, and dozens more
- Character profiles, location notes, and research materials alongside your outline
Annual at $25/year. Lifetime at $199 one-time. Both remarkably cheap compared to subscription alternatives.
Ratings: Capterra: 4.5/5 (170+ reviews).
AI features are limited compared to Sudowrite or Novelcrafter. Plottr focuses on the planning phase rather than drafting. But for writers who need structure before they can write, Plottr fills a gap that no AI writing tool covers well on its own.
How to choose
Writing fiction? Start with Sudowrite for drafting and voice matching, then edit with ProWritingAid. Use Plottr if you need to outline first.
Writing non-fiction? Use Claude for drafting and structural analysis. Its 200K context window handles entire manuscripts. Edit with ProWritingAid.
Want maximum control? Novelcrafter's Codex system gives you the most structured AI-assisted writing experience. Higher learning curve, better long-term results.
On a tight budget? ChatGPT's free tier handles brainstorming and outlining. Claude's free tier covers limited drafting. ProWritingAid's $10/month annual plan covers editing. Total: $10/month.
Need speed above all? Squibler generates rough drafts fastest. Quality requires heavy editing, but you'll have words on the page in hours instead of months.
One thing every tool has in common: the output needs your editing. AI-generated prose without human revision reads like AI-generated prose. Readers know it, Amazon's algorithms might flag it, and your name is on the cover. Use these tools to write faster, not to avoid writing.
FAQ
Can I publish an AI-written book on Amazon KDP?
Yes, but with requirements. Amazon KDP requires you to disclose AI-generated content during the publishing process. You must indicate whether AI was used to create text or images. Fully AI-generated books without disclosure risk removal. The practical standard: use AI as a tool in your process, edit the output substantially, and disclose honestly. Most successful indie authors using AI treat it as a drafting assistant, not a ghostwriter.
Which AI writes the most natural-sounding prose?
Claude produces the most natural long-form prose among general-purpose AI tools. For fiction specifically, Sudowrite's voice matching feature comes closest to replicating a specific author's style. ChatGPT tends toward repetitive sentence patterns in long-form output. All AI-written prose benefits from human editing to add personality, remove generic phrasing, and fix rhythm.
Is Sudowrite worth it for non-fiction?
Not really. Sudowrite's features (Story Engine, voice matching, scene description) are optimized for fiction. For non-fiction, you're paying for capabilities you won't use. Claude at $20/month gives you better non-fiction output with a context window large enough to hold your entire manuscript. If you write both fiction and non-fiction, consider Novelcrafter as a middle ground.
How long does it take to write a book with AI?
A rough first draft of a 50,000-word novel can be generated in 1-3 days using Squibler or Sudowrite's Story Engine. But that raw draft requires 2-4 weeks of serious editing to reach publishable quality. Realistic total timeline: 4-8 weeks for a genre fiction novel, 6-12 weeks for non-fiction, using AI throughout the process. Without AI, the same projects typically take 3-12 months. The time savings come from drafting speed and brainstorming efficiency, not from skipping the editing phase.
Do I need to learn prompt engineering to use these tools?
Not for purpose-built tools like Sudowrite, Novelcrafter, or Squibler. They have structured interfaces that guide you through providing the right information. For ChatGPT and Claude, basic prompt skills help significantly. Telling Claude "write chapter 3 of my self-help book in a conversational tone, targeting first-time managers, about delegating effectively" produces much better results than "write about delegation." Our guide to talking to AI covers the fundamentals.
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