The best AI writing tools for authors depend on the job. General assistants such as ChatGPT, Claude and Google Gemini are the most flexible for brainstorming, outlining, feedback and blurbs; research tools such as Perplexity are better when you need sources you can check; and dedicated editing tools such as Grammarly and ProWritingAid are better for line-by-line grammar and style. Most authors need one general assistant and, at most, one specialist tool.

This guide includes a few product links near the end. As an Amazon Associate, Freyja Publishing earns from qualifying purchases, at no extra cost to you.

This guide compares the main options by the stage of the writing and publishing process where each helps most, explains what they cost at the time of writing, and covers the rules and risks every author should know before using AI: retailer disclosure, copyright and privacy. It assumes you write the book yourself and use AI as an assistant.

At a glance

• One general assistant covers most needs. ChatGPT, Claude and Gemini all brainstorm, outline, critique and draft marketing copy; the differences are in style, long-document handling and which ecosystem you already use.
• Paid plans cluster around US$20 a month at the time of writing (October 2026), and all three have free tiers. Prices change and may exclude tax.
• Use AI for planning, feedback and admin, not your voice. Readers notice generic prose, and heavy reliance makes books sound alike.
• Disclosure rules apply. KDP requires you to declare AI-generated text, images and translations; AI-assisted editing and brainstorming do not need declaring.
• Verify every fact. AI tools can state wrong information confidently, including invented sources.

Disclosure: this article contains a referral link to Claude. If you sign up through it, Freyja Publishing may receive Claude usage credit, at no extra cost to you. It does not change what we recommend. See our affiliate disclosure.

Want to try the AI assistant we use for book work? Claude handles long manuscripts well, which makes it useful for outlining, editing passes and keeping series notes straight. You can start on the free plan.

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The tools compared

Tool	Type	Strongest for authors at	Free tier	Paid plan (at the time of writing)
ChatGPT (OpenAI)	General assistant	Brainstorming, outlining, marketing copy, quick questions	Yes, with limits	ChatGPT Plus about US$20/month
Claude (Anthropic)	General assistant	Working with long manuscripts, editorial feedback, consistency checks	Yes, with limits	Claude Pro about US$20/month
Google Gemini	General assistant	Authors who work in Google Docs and Gmail	Yes, with limits	Google AI Pro about US$19.99/month
Perplexity	Search and research assistant	Research with cited sources you can check	Yes, with limits	Perplexity Pro about US$20/month
Grammarly	Editing assistant	Grammar, clarity and tone while you type	Yes	Paid plans available; check current pricing
ProWritingAid	Editing assistant	Manuscript-level style reports for fiction and non-fiction	Yes	Paid plans available; check current pricing

Prices change often and differ by country and billing period, so check each provider before subscribing. Plans also change which models and usage limits you get, so compare the current plan details rather than relying on the price alone.

ChatGPT

ChatGPT is the most widely used general assistant and a strong all-rounder. It is quick at producing lists of ideas, titles, chapter outlines and alternative phrasings, and it handles marketing tasks such as ad variations and social posts well. It can also work with uploaded files and images. For a full beginner’s walkthrough, see getting started with ChatGPT.

Claude

Claude, made by Anthropic, is often chosen by authors for editorial work on long documents. It can take in a large amount of text at once, which makes it useful for feedback on whole chapters, checking a series bible against a manuscript, or tracking timelines and character details. Many writers find its default prose style less formulaic, though any AI output still needs your edit.

Try Claude: Get started with Claude here. (Referral link: if you sign up, Freyja Publishing may receive Claude usage credit. It costs you nothing extra.)

If you are choosing between the two most popular assistants, Claude vs ChatGPT for authors compares them task by task.

Google Gemini

Gemini is built into Google’s products. If you already draft in Google Docs and manage email in Gmail, it can work inside those tools, which saves copying text back and forth. Its usefulness for creative feedback is broadly similar to the other general assistants; the integration is the main reason to choose it.

Perplexity

Perplexity combines search with AI summaries and shows the sources it used. That makes it a better starting point than a general chatbot for research, because you can open and check each source. It is still a starting point: read the original sources before relying on anything.

Grammarly and ProWritingAid

These are editing tools rather than general assistants. Grammarly works as you type across many apps and is strong on grammar, clarity and tone. ProWritingAid produces detailed reports on a manuscript, such as overused words, sentence variety and pacing. Both now include generative AI features as well. How they compare is covered in ProWritingAid vs Grammarly.

Which tool for which stage

Stage	Good uses of AI	Best-suited tools	Keep human
Ideas and planning	Premise variations, trope lists, “what if” questions, chapter outlines	Any general assistant	Choosing the idea and the angle
Research	Finding sources, summarising long documents, building question lists	Perplexity, then a general assistant for summaries	Checking every fact against the original source
Drafting	Getting unstuck, suggesting what a scene needs, describing options	A general assistant, used sparingly	The actual prose and voice
Self-editing	Feedback on pacing, clarity, continuity and character consistency	Claude or another assistant for long text; ProWritingAid or Grammarly for line-level checks	Deciding which feedback to accept
Publishing	Blurb drafts, keyword brainstorming, metadata descriptions	Any general assistant	Final wording, accuracy and category choices
Marketing	Email drafts, social post ideas, ad copy variations	ChatGPT, Claude or Gemini	Anything sent in your name

For publishing tasks such as keywords and categories, AI can generate options quickly, but the choices still need checking against how readers actually search; the KDP keywords and categories guide explains how. For a professional edit, AI feedback is a supplement, not a substitute; the self-editing guide covers what to do before and after.

A practical workflow

1. Start with one general assistant on the free tier. Use it for a few weeks across planning, feedback and marketing tasks before paying for anything.
2. Set it up for your book. Many tools let you save background information in a project or custom instructions: genre, audience, series details, style preferences. This makes answers far more useful.
3. Plan with AI, write yourself. Use it to test structure and spot gaps in an outline, then draft in your own words.
4. Ask for critique, not rewrites. “What is unclear in this chapter?” teaches you more and keeps your voice intact. “Rewrite this” replaces your voice with the tool’s.
5. Use it for continuity checks. Ask it to list character details, dates or timeline events from your manuscript and compare them with your notes.
6. Draft the admin. Blurbs, author bios, email newsletters and ad variations are well suited to AI first drafts that you then edit.
7. Verify and edit everything. Treat output as a draft from a fast but unreliable assistant.
8. Upgrade only if you hit limits. Pay for a plan when the free tier is genuinely slowing you down, and review the subscription regularly.

Rules and risks to know before you start

Retailer disclosure

KDP’s content guidelines distinguish between AI-generated content (text, images or translations created by an AI tool, even if you edit them afterwards) and AI-assisted content (work you created yourself and used AI to edit, refine, check or brainstorm). You must declare AI-generated content when you publish or republish a book; AI-assisted use does not need declaring. Other retailers and distributors have their own policies, so check each one you use.

Copyright

Copyright protects human authorship. The US Copyright Office’s 2025 report on copyrightability concluded that purely AI-generated material is not protected, while human-written text and human creative choices can be. Other countries are still developing their positions. The more of the book that is genuinely yours, the clearer your rights. For more on rights and contracts, see the guide to publishing rights.

Accuracy

AI tools can produce plausible but false statements, including statistics, quotes and references that do not exist. In non-fiction, every factual claim needs checking against a reliable original source. In fiction, check real-world details such as places, history and procedures.

Privacy and your manuscript

Before uploading unpublished work, check each tool’s privacy settings and terms, including whether your conversations may be used to improve the provider’s models and how to opt out. Avoid uploading other people’s confidential material, such as a client manuscript, without permission.

Your voice

AI output tends towards common phrasings and predictable structures. If many passages in your book come from AI drafts, the book is likely to sound like many others. Readers buy authors for their voice.

Common mistakes

• Paying for several tools at once. The general assistants overlap heavily. Start with one.
• Accepting rewrites wholesale. It flattens your voice and can introduce errors.
• Trusting facts without checking. Invented references and wrong figures are a known weakness.
• Skipping the disclosure question. Declaring AI-generated content on KDP is a requirement, not an option.
• Using AI for cover art without checking rules and rights. AI images must be declared on KDP, and some stores and readers respond badly to them.
• Vague prompts. “Make this better” gives generic results. Say what you want: shorter, clearer, more tension, a different point of view.
• Replacing professional editing. AI feedback is useful, but it does not replace an experienced editor’s judgement.

For a wider view of where AI fits in publishing, see how AI is transforming self-publishing. For AI assistants alongside every other piece of author software, see the author toolkit guide.

Sources this guide draws on: the official plan and pricing pages of OpenAI, Anthropic, Google, Perplexity, Grammarly and ProWritingAid; Amazon KDP’s content guidelines on AI-generated content; and the US Copyright Office’s 2025 report on copyright and artificial intelligence (copyrightability), checked in October 2026.

Frequently asked questions

What is the best AI tool for writing a book?

For most authors, a general assistant such as Claude, ChatGPT or Gemini is the most useful single tool, because it helps with planning, feedback and marketing. Writers who work mainly on long manuscripts often prefer Claude; those in Google’s ecosystem may prefer Gemini. Try the free tiers before paying.

Is it allowed to use AI to write a book for Amazon?

Yes, but KDP requires you to declare AI-generated text, images and translations when you publish. Using AI only to brainstorm, edit or check your own writing counts as AI-assisted and does not need declaring.

Can I copyright a book written with AI?

In the United States, the parts you write and the creative choices you make can be protected, but material generated entirely by AI is not, according to the US Copyright Office. Rules in other countries are still developing, so keep the creative work your own.

Is ChatGPT or Claude better for authors?

Both are capable. ChatGPT is a fast all-rounder, especially for ideas and marketing copy; Claude is often preferred for feedback on long manuscripts and consistency checks. The detailed comparison is in the Claude vs ChatGPT guide linked above.

Do I still need Grammarly or ProWritingAid if I use an AI assistant?

Not necessarily. A general assistant can review grammar and style when asked, but dedicated editing tools check every sentence as you work and produce structured reports. Many authors find one of each is enough.

Will AI tools use my manuscript for training?

It depends on the provider, plan and your settings. Check each tool’s privacy settings and terms before uploading unpublished work, and opt out of training where that option is offered and you prefer it.

AI tools are most valuable when they save time on the work around your writing: planning, checking, and the endless admin of publishing. Choose one assistant, learn it well, keep the words your own, and verify everything that matters.