Add Fern Writer capabilities and customization documentation

fern/products/docs/pages/ai/writer.mdx

@@ -38,6 +38,72 @@ Request changes by commenting in the Slack thread or directly on the PR. Fern Wr
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+## Capabilities
+
+Fern Writer goes beyond simple text edits. Because it understands your repository structure, Fern's component library, and your site's navigation configuration, it can handle a wide range of documentation tasks.
+
+### Write and update content
+
+Fern Writer can create new pages from scratch or edit existing ones. Give it a topic, a GitHub pull request, or a GitHub issue, and it will draft documentation that fits your existing style and structure.
+
+- **Draft new pages** for features, guides, tutorials, or reference material
+- **Add sections** to existing pages, such as new parameters, examples, or FAQs
+- **Update outdated content** like version numbers, renamed fields, or deprecated features
+- **Fix errors** in code examples, broken links, or inaccurate descriptions
+
+### Use Fern components
+
+Fern Writer knows how to use the full [Fern component library](/learn/docs/writing-content/components/overview). It can add and edit components like [Callouts](/learn/docs/writing-content/components/callouts), [Cards](/learn/docs/writing-content/components/cards), [Code blocks](/learn/docs/writing-content/components/code-blocks), [Steps](/learn/docs/writing-content/components/steps), [Tabs](/learn/docs/writing-content/components/tabs), [Accordions](/learn/docs/writing-content/components/accordions), and more. You don't need to specify which components to use — Fern Writer selects the right ones based on the content.
+
+### Reorganize and restructure
+
+Fern Writer can modify your site's navigation and page organization, not just page content.
+
+- **Merge or split pages** to improve information architecture
+- **Move content between pages** while preserving cross-references
+- **Add redirects** so existing links continue to work after restructuring
+- **Update navigation configuration** in your `docs.yml` and product YAML files
+
+### Review and improve quality
+
+Ask Fern Writer to review your docs for issues that are hard to catch manually across many pages.
+
+- **Check for inconsistencies** in terminology, formatting, or tone across pages
+- **Apply style changes across pages**, such as renaming a product or updating terminology site-wide
+- **Improve clarity** by rewriting confusing sections or adding missing context
+
+### Work from external context
+
+Fern Writer can incorporate information from sources beyond your docs repository.
+
+- **Document features from GitHub PRs** by reading the code changes and writing corresponding documentation
+- **Act on GitHub issues** by reading issue descriptions and making the requested documentation updates
+- **Process Slack thread context** — when tagged in an existing thread, it reads the full conversation before responding
+- **Use image and file attachments** shared in Slack for additional context
+
+### Iterate on feedback
+
+Fern Writer treats every pull request as a conversation. After it opens a PR, you can request changes in two ways:
+
+- **Reply in the Slack thread** where the PR was created
+- **Comment directly on the GitHub PR**, including inline code comments
+
+Fern Writer responds to feedback from both humans and automated review tools such as linters or CI checks. It continues iterating until the PR meets your requirements.
+
+## Customize with AGENTS.md
+
+Add an `AGENTS.md` file to the root of your docs repository to customize how Fern Writer behaves. This file lets you define project-specific guidelines that Fern Writer follows when making changes.
+
+Use `AGENTS.md` to specify:
+
+- **Writing style and tone** — formal vs. conversational, active vs. passive voice, preferred terminology
+- **Structural conventions** — how pages are organized, required sections, heading hierarchy
+- **Component preferences** — when to use specific Fern components like Callouts vs. Asides
+- **Terminology rules** — product names, feature names, and terms that must be used consistently
+- **Files or directories to avoid** — content that Fern Writer shouldn't modify
+
+Fern Writer reads this file before every task, so updates take effect immediately without reinstallation.
+
 ## Setup
 
 To start using Fern Writer, add it to your Slack workspace (you must be a Slack admin) and invite it to channels where your team discusses documentation.