Athens

Best AI Writing Tools for Substack Writers

- Moritz Wallawitsch

Substack has no built-in AI. No grammar checker, no rewriting assistant, no brainstorming sidebar. The editor is intentionally minimal. That is part of the appeal. But it also means that if you want AI help with your newsletter, you need to bring your own tools.

Most writers start with ChatGPT. They paste a draft into the chat, ask for feedback, copy the rewritten version back into Substack. It works in the sense that words appear on the screen. But the workflow is terrible. Formatting breaks. Your voice gets flattened. You spend more time fixing the output than you saved generating it.

The problem is not AI itself. The problem is the copy-paste loop. Every time you move text between a chatbot and Substack, you lose formatting, context, and control. The best AI writing tools for Substack writers are the ones that eliminate that loop entirely. They let you write, edit with AI, and export to Substack in a single workflow.

Here are six tools that actually work for newsletter writers, ranked by how well they fit into a Substack publishing workflow.

  1. Athens
  • Write and Edit with AI, Export to Substack

$99/year | Free tier available

Athens is a writing editor with AI editing built directly into the document. You write in a clean WYSIWYG markdown editor. When you want AI help, you highlight a section and give an instruction. The AI proposes changes inline with color-coded diffs. Green for additions, red strikethrough for deletions. You accept or reject each change individually.

This solves the core problem Substack writers face. You do not leave your editor. You do not copy text into a chatbot and paste it back. You do not lose formatting. The AI works on your actual document, in context, and you see exactly what it wants to change before anything is committed.

For Substack specifically, the export workflow is the key advantage. Athens stores your document in markdown and exports clean HTML. You paste that HTML into Substack's editor and everything renders correctly on the first try. Headings, bold text, lists, links, block quotes. No broken formatting. No manual cleanup.

Compare this to the ChatGPT workflow: write in ChatGPT, copy, paste into Substack, discover that all the formatting is broken, manually re-bold every heading, re-create every list, fix every link. Athens eliminates all of that. If you have dealt with the ChatGPT-to-Substack formatting problem, you know how much time this saves.

Why Substack writers choose it:

  • AI edits your existing draft instead of generating from scratch. Your newsletter voice stays intact.
  • Inline diffs show exactly what the AI changed. You control every word that gets published.
  • Clean HTML export pastes directly into Substack without formatting issues.
  • No copy-paste loop. No context-switching between windows.
  • $99/year is less than most Substack writers earn from a single paid subscriber.

Limitations: Athens is a writing and editing tool. It does not do research or SEO analysis. You will want a separate research tool if your newsletter is research-heavy.

2. ChatGPT and Claude - Brainstorming, Feedback, Research

$20/month each | Free tiers available

General-purpose AI chatbots are still useful for Substack writers. Just not as editors. ChatGPT and Claude are excellent at brainstorming newsletter topics, pressure-testing arguments, generating outlines, and answering research questions. If you are stuck on what to write this week, a ten-minute conversation with Claude will give you three solid angles you had not considered.

The problem comes when you try to use them as writing tools. You paste your draft into the chat. The AI rewrites it. You copy the rewritten version. You paste it into Substack. The formatting is gone. The markdown syntax shows up as literal asterisks and hash symbols. Your carefully structured post looks like a broken config file.

Even if you ask ChatGPT to output HTML instead of markdown, you are now reading raw HTML in a chat window. You cannot tell if the content is good because it is buried in tags. And one missing closing tag will wreck your Substack layout.

Best for: The thinking phase. Brainstorming topics, testing arguments, getting feedback on ideas before you start writing. Also useful for research questions where you need a quick synthesis of a complex topic.

Not great for: Anything that requires getting text into Substack. The copy-paste workflow between chatbots and Substack is fundamentally broken. Use chatbots for thinking, not for producing publishable text.

3. Grammarly - Grammar Baseline Inside Substack

Free | Premium at $12/month

Grammarly is the one AI writing tool that actually works inside Substack's editor. The browser extension detects the Substack compose window and underlines errors as you type. Spelling mistakes, grammar issues, awkward phrasing. You click an underlined word, accept or ignore the suggestion, and keep writing. No copy-paste. No context-switching. No export step.

For many Substack writers, Grammarly is enough. If you are a confident writer who just needs a safety net for typos and comma splices, the free tier catches the obvious mistakes. Premium adds tone detection and sentence rewrites, but the free version handles the basics well.

The limitation is depth. Grammarly works at the sentence level. It will not help you restructure an argument, tighten a 2,000-word post into 1,200 words, or suggest a better opening paragraph. It catches surface errors. It does not improve your writing at a structural level.

Best for: Writers who want a grammar safety net without leaving Substack's editor. The browser extension approach means zero workflow disruption.

Not great for: Substantive editing. If you need help with structure, clarity, or voice, Grammarly will not get you there. It is a proofreader, not an editor.

4. Notion AI - If You Already Draft in Notion

$10/month add-on | Requires Notion subscription

Many newsletter writers draft in Notion before moving to Substack. If you are already in that camp, Notion AI lets you highlight a block of text and ask the AI to rewrite it, summarize it, or change the tone. The AI edits appear directly in your Notion document. No chat window. No copy-paste into a separate tool.

The workflow is straightforward: draft in Notion with AI assistance, then copy the finished post into Substack. For plain text and basic formatting, the copy-paste from Notion to Substack works reasonably well. Notion's clipboard output is rich text, and Substack's editor accepts it without mangling the structure.

The problem is images and embeds. If your newsletter includes screenshots, diagrams, or embedded content, the Notion-to-Substack paste breaks. Images do not transfer. You have to re-upload them manually in Substack. Tables get flattened. Code blocks lose their formatting. For text-heavy newsletters, Notion AI works. For anything visually rich, the transfer is painful.

Best for: Writers who already use Notion as their second brain and want AI editing without adding another tool to their workflow.

Not great for: Writers who do not already use Notion. Adding a $10/month AI feature to a tool you only use for drafting is expensive compared to purpose-built alternatives.

5. Perplexity - Research with Citations

$20/month | Free tier available

Perplexity is not a writing tool. It is a research tool. But for Substack writers who publish research-heavy newsletters, it is one of the most useful AI tools available. You ask a question, and Perplexity gives you an answer with inline citations to real sources. You can see exactly where each claim comes from and click through to the original article, study, or report.

This is a massive upgrade over using ChatGPT for research. ChatGPT will confidently state facts without telling you where they came from. Perplexity shows its sources. For a newsletter writer whose credibility depends on accuracy, that difference matters.

The typical workflow: use Perplexity to research your topic, gather sources and key data points, then switch to your writing tool to draft the actual newsletter. Perplexity does not help you write. It helps you know what to write about and gives you the evidence to back it up.

Best for: The research phase of newsletter writing. Especially useful for newsletters about technology, science, finance, or any topic where readers expect cited claims.

Not great for: Actual writing or editing. Perplexity answers questions. It does not draft, rewrite, or polish newsletter posts.

6. Hemingway Editor - Quick Readability Check Before You Publish

Free web version | Desktop app $19.99 one-time

Hemingway Editor does one thing: it tells you when your writing is hard to read. Paste your draft into the web app and it highlights sentences that are too long, words that are too complex, and uses of passive voice. Each issue gets a color. Yellow means a sentence is dense. Red means it is nearly unreadable. Blue means you used an adverb. Green means passive voice.

For newsletter writers, Hemingway is a useful final check. After you finish drafting and editing, paste your post into Hemingway and scan for red and yellow highlights. If a sentence is flagged red, it probably needs to be split into two sentences or simplified. Newsletter readers skim. Short, clear sentences keep them reading. Long, complex sentences make them close the tab.

The limitation is the same as Grammarly: Hemingway works at the surface level. It can tell you a sentence is too long, but it cannot tell you if your argument is weak or your structure is confusing. It is a readability checker, not an editor. Use it as a final pass, not as your primary editing tool.

Best for: A quick readability scan before hitting publish. Especially useful if you tend to write long, complex sentences. The free web version is enough for most newsletter writers.

Not great for: Substantive editing, structural feedback, or anything beyond sentence-level readability.

What Substack Writers Actually Need

The ideal AI workflow for a Substack writer looks like this: brainstorm and research in one tool, write and edit in another, then publish on Substack with zero formatting friction. No copy-paste chains. No manual reformatting. No reading raw HTML in a chat window.

Most writers cobble together a version of this by accident. They research in ChatGPT, draft in Google Docs, edit by copying paragraphs into Claude, paste the result into Substack, then spend twenty minutes fixing the formatting. Every step introduces friction. Every paste risks breaking something.

The tools above simplify this. Perplexity handles research with real citations. Athens handles writing and AI editing in one place, then exports clean HTML to Substack. Grammarly catches typos directly inside Substack's editor. Hemingway gives your final draft a readability pass.

The key insight is that the best AI writing tool for Substack is not a chatbot. Chatbots are great at thinking tasks: brainstorming, research, feedback on ideas. They are terrible at producing text that lands cleanly in Substack's editor. The formatting problem is not a minor annoyance. It is a workflow-killer that eats the time AI was supposed to save.

The Cost Comparison

Here is what a complete AI writing stack costs for a Substack writer:

  • Athens: $99/year ($8.25/month) for writing and AI editing with clean Substack export.
  • Perplexity: Free tier for occasional research. $20/month if you need unlimited pro searches.
  • Grammarly: Free for basic grammar. $12/month for premium suggestions.
  • Hemingway: Free web version. No subscription needed.

Minimum cost: $8.25/month (Athens alone). Maximum cost with everything: around $40/month. Compare that to paying $20/month for ChatGPT Plus and still spending twenty minutes reformatting every post.

If your newsletter has even a handful of paid subscribers, these tools pay for themselves in the first month. If it does not have paid subscribers yet, the time you save on formatting and editing can go toward writing the posts that attract them.

Getting Started

If you are currently writing your newsletter in Substack's editor with no AI assistance, start with one tool. Not six. Pick the one that solves your biggest problem.

  • If your biggest problem is editing: Try Athens. Write your next post in the editor, use AI to tighten and polish it, then export to Substack.
  • If your biggest problem is typos: Install Grammarly. It works inside Substack with zero setup.
  • If your biggest problem is research: Try Perplexity for your next research-heavy post. The citations alone are worth the free tier.
  • If your biggest problem is readability: Paste your next draft into Hemingway before you publish. Fix the red highlights.

You do not need all six tools. Most Substack writers will get the biggest improvement from Athens plus Grammarly. The AI editing handles structure and clarity. The grammar checker handles the surface errors. And the clean export to Substack means you never fight with formatting again.

For more on building a complete AI writing workflow, see our guide on how to write a newsletter with AI. And if you are coming from the ChatGPT copy-paste workflow, our ChatGPT-to-Substack formatting guide explains exactly why it breaks and how to fix it. For a broader comparison of writing apps that work well with Substack, see our best writing apps for Substack roundup.