> For clean Markdown content of this page, append .md to this URL. For the complete documentation index, see https://buildwithfern.com/learn/llms.txt. # Docs commands > Complete reference for all Fern CLI commands for generating and managing documentation. These commands build, preview, and publish a Fern documentation site, and validate the MDX pages and links behind it. Creating a docs project with `fern init --docs` and validating `docs.yml` with `fern check` are [general commands](/learn/cli-api-reference/cli-reference/general-commands), and [SDK commands](/learn/cli-api-reference/cli-reference/sdk-commands) generate client libraries from the same API definition your docs render. Each docs command accepts the [global options](/learn/cli-api-reference/cli-reference/options). | Command | Description | | ------------------------------------------------------- | ------------------------------------------------------------------------ | | [`fern docs dev`](#fern-docs-dev) | Run local documentation preview server | | [`fern docs diff`](#fern-docs-diff) Beta | Generate visual diffs between preview and production docs | | [`fern generate --docs`](#fern-generate---docs) | Build & publish documentation updates | | [`fern docs preview list`](#fern-docs-preview-list) | List all preview deployments | | [`fern docs preview delete`](#fern-docs-preview-delete) | Delete a preview deployment | | [`fern docs md check`](#fern-docs-md-check) | Validate MDX syntax in documentation files | | [`fern docs md generate`](#fern-docs-md-generate) | Generate MDX pages from library source code | | [`fern docs theme export`](#fern-docs-theme-export) | Export theme-eligible fields from `docs.yml` into a standalone directory | | [`fern docs theme upload`](#fern-docs-theme-upload) | Upload a theme to Fern's registry | | [`fern docs link check`](#fern-docs-link-check) | Check for broken links on a live documentation site | | [`fern docs theme list`](#fern-docs-theme-list) | List all themes for your organization | | [`fern mcp install`](#fern-mcp-install) | Connect a coding agent to your organization's Fern MCP server | ## Detailed command documentation #### fern generate --docs Use `fern generate --docs` to create a documentation site for your API. #### terminal ```bash fern generate --docs [--instance ] [--preview] [--id ] [--force] ``` ### instance Use `--instance` to specify which instance URL in your `docs.yml` to generate documentation for. ```bash fern generate --docs --instance your-organization.docs.buildwithfern.com ``` ### preview Use `--preview` to preview updates to your documentation before publishing changes to your production site. ```bash fern generate --docs --preview ``` ### id Use `--id` with `--preview` to create a stable, named preview link. The preview URL follows the format `{org}-preview-{id}.docs.buildwithfern.com`, so rerunning with the same `--id` updates the existing preview in place rather than creating a new one. ```bash fern generate --docs --preview --id my-feature # -> https://your-org-preview-my-feature.docs.buildwithfern.com ``` This is useful in CI workflows where you want one preview URL per pull request. See [Preview changes](/learn/docs/preview-publish/preview-changes#preview-links) for details. ### force When reusing an `--id` that already exists, Fern prompts you to confirm the overwrite. Use `--force` to skip the confirmation. This is detected automatically in GitHub Actions, but is needed for other CI environments like Azure Pipelines. ```bash fern generate --docs --preview --id my-feature --force ``` #### fern docs dev Use `fern docs dev` to run a local development server to preview your docs. #### terminal ```bash fern docs dev [--port ] ``` #### Windows: enable long path support On Windows, `fern docs dev` requires [long path support](https://learn.microsoft.com/en-us/windows/win32/fileio/maximum-file-path-limitation#enable-long-paths-in-windows-10-version-1607-and-later) to be enabled. To enable long path support, run the following command in an elevated PowerShell prompt, then restart your terminal: ```powershell New-ItemProperty -Path 'HKLM:\SYSTEM\CurrentControlSet\Control\FileSystem' -Name 'LongPathsEnabled' -Value 1 -PropertyType DWORD -Force ``` If you can't enable long path support, use [Windows Subsystem for Linux (WSL)](https://learn.microsoft.com/en-us/windows/wsl/install) to run `fern docs dev` in a Linux environment instead. ### port Use `--port ` to specify the port the docs preview will be run on. ```bash fern docs dev --port 57908 ``` #### fern docs diff Beta Use `fern docs diff` to generate visual diffs between your preview deployment and production docs. This command is intended for use in [GitHub Actions](https://github.com/fern-api/docs/blob/main/.github/workflows/preview-docs.yml). It captures screenshots of both versions and creates side-by-side comparison images. #### terminal ```bash fern docs diff [--output ] ``` Pass the preview URL from `fern generate --docs --preview` and one or more MDX file paths. Diff images are saved to `.fern/diff` by default. ```bash fern docs diff acme-preview-abc123.docs.buildwithfern.com fern/pages/intro.mdx fern/pages/quickstart.mdx ``` ### output Use `--output` to specify a custom directory for diff images. ```bash fern docs diff acme-preview-abc123.docs.buildwithfern.com fern/pages/intro.mdx --output ./my-diffs ``` #### fern docs preview list Use `fern docs preview list` to list all [preview deployments](/learn/docs/preview-publish/preview-changes#manage-preview-links) for your organization. #### terminal ```bash fern docs preview list [--limit ] [--page ] ``` ### limit Use `--limit` to specify the number of preview deployments to display per page. ```bash fern docs preview list --limit 20 ``` ### page Use `--page` to specify which page of results to display. ```bash fern docs preview list --page 2 ``` #### fern docs preview delete Use `fern docs preview delete` to delete a [preview deployment](/learn/docs/preview-publish/preview-changes#manage-preview-links) generated with `fern generate --docs --preview`. Pass the full preview URL, or use `--id` to delete by the identifier used during generation. #### terminal ```bash fern docs preview delete # Or delete by preview ID fern docs preview delete --id ``` ### id Use `--id` to delete a preview deployment by the identifier used during generation instead of the full preview URL. ```bash fern docs preview delete --id ``` #### fern docs md check Use `fern docs md check` to validate MDX syntax across all documentation pages referenced in your navigation configuration, including `docs.yml`, versioned configuration files, and product-specific YAML files. #### terminal ```bash fern docs md check ``` The command parses each MDX file and reports syntax errors with file paths and line:column numbers. The command accounts for frontmatter offsets, so reported line numbers correspond to the actual lines in your file. ```plaintext fern/pages/quickstart.mdx:12:5 Unexpected closing tag, expected corresponding closing tag for `` fern/pages/guide.mdx:45:1 Expected a closing tag for `` before the end of `paragraph` ``` When all files are valid, you'll see a success message: ```plaintext ✓ All 42 MDX files are valid ``` #### fern docs md generate Use `fern docs md generate` to generate [MDX documentation pages from your library source code](/learn/docs/api-references/library-reference). The command reads `libraries` entries in `docs.yml` and produces pages for modules, classes, functions, and types. #### terminal ```bash fern docs md generate [--local] [--library ] ``` By default, the command sends the repository URL of a `git` input to Fern's servers for parsing. Pass `--local` to parse the source on your machine instead. ### local Use `--local` to parse library source locally rather than on Fern's servers. Required when the library uses a `path` input, and supported for `git` inputs. Local generation does not require authentication. ```bash fern docs md generate --local ``` ### library Use `--library` to generate docs for a single library when multiple libraries are configured. ```bash fern docs md generate --library plant-sdk ``` When `--library` is omitted, all configured libraries are processed in parallel. #### fern docs theme export Use `fern docs theme export` to extract the [theme-eligible fields](/learn/docs/customization/global-themes) from your `docs.yml` into a standalone directory. The exported `theme.yml` and its assets can then be uploaded with `fern docs theme upload`. #### terminal ```bash fern docs theme export [--output ] ``` By default, files are written to `./fern/theme/`. ### output Use `--output` to specify a custom directory for the exported theme. ```bash fern docs theme export --output ./my-theme ``` #### fern docs theme upload Use `fern docs theme upload` to upload a [theme](/learn/docs/customization/global-themes) to Fern's registry. The command reads `theme.yml` from `./fern/theme/` and uploads it along with any referenced file assets. #### terminal ```bash fern docs theme upload [--name ] [--org ] ``` ### name Use `--name` to set the theme name. Defaults to `default`. ```bash fern docs theme upload --name my-theme ``` ### org Use `--org` to override the organization ID from `fern.config.json`. ```bash fern docs theme upload --org my-org ``` #### fern docs link check Use `fern docs link check` to scan a live documentation site for broken links. The command crawls the published site, checks every link, and reports broken (404) and blocked (403) URLs along with their source pages. #### terminal ```bash fern docs link check [--url ] [--output ] ``` Unlike the [`broken-links` rule](/learn/cli-api-reference/cli-reference/general-commands#fern-check) in `fern check`, which validates only internal links in your local YAML navigation tree, `fern docs link check` checks all links — internal and external — on your live deployed site. By default, the command auto-detects your docs URL from the `instances` in `docs.yml`. When all links are valid, the command exits with a success message. The command first scrapes every page on the site, then checks each link it finds. When broken links are found, the output includes a summary and a grouped list of broken URLs with status codes and source file paths. ```plaintext ◆ Checking links on your-org.docs.buildwithfern.com... Scraping pages [████████████████████] 100% | 42/42 Checking links [████████████████████] 100% | 240/240 Finished in 2 minutes, 23 seconds Summary Pages scanned 42 Links checked 240 ✓ Working 228 ✗ Broken 8 (external) ⚠ Blocked 4 ───────────────────────────────────── External Broken Links (8) ✗ https://example.com/removed-page → 404 fern/pages/quickstart.mdx fern/pages/overview.mdx ✗ https://example.com/old-endpoint → 404 fern/pages/integrations.mdx ``` ### url Use `--url` to specify which docs site to check. This is useful when you have multiple instances or want to check a preview deployment. ```bash fern docs link check --url https://your-org.docs.buildwithfern.com ``` ### output Use `--output` to control the output format. Supported values are `text` (default), `json`, and `csv`. ```bash # JSON output for programmatic use fern docs link check --output json # CSV output for spreadsheets or reporting fern docs link check --output csv ``` #### fern docs theme list Use `fern docs theme list` to list all [themes](/learn/docs/customization/global-themes) uploaded for your organization. #### terminal ```bash fern docs theme list [--json] [--org ] ``` By default, outputs one theme name per line. ### json Use `--json` to output the full list as a JSON array, including `updatedAt` timestamps. ```bash fern docs theme list --json ``` ### org Use `--org` to override the organization ID from `fern.config.json`. ```bash fern docs theme list --org my-org ``` #### fern mcp install Use `fern mcp install` to register [your organization's Fern MCP server](/learn/docs/ai-features/fern-mcp-servers) with a coding agent, giving it Fern's own documentation and configuration reference alongside your live sites, deployments, analytics, and reader activity — the same tools [Fern Agent](/learn/docs/ai-features/fern-agent) works from. #### terminal ```bash fern mcp install [--client claude|cursor|codex] [--org ] ``` The command configures every supported agent installed on the machine, adding a `fern` server entry that holds the server URL and an `Authorization` header. Other entries and surrounding content in each file are preserved. | Client | Config file | | ----------- | ---------------------- | | Claude Code | `~/.claude.json` | | Cursor | `~/.cursor/mcp.json` | | Codex | `~/.codex/config.toml` | The token doesn't refresh, so re-run `fern login && fern mcp install` if the agent's Fern tools start failing. ### client Use `--client` to configure specific agents instead of every one detected. Repeat the flag to name more than one. ```bash fern mcp install --client claude --client cursor ``` ### org Use `--org` to override the organization ID from `fern.config.json`. The organization scopes the server URL to `https://fai.buildwithfern.com/organizations//mcp`. Outside a Fern project, the command falls back to the unscoped `https://fai.buildwithfern.com/mcp`. ```bash fern mcp install --org my-org ```