docusaurus plugin-content-docs "Error: plugin not found" build failed

Fix Docusaurus plugin-content-docs "plugin not found" failures

TL;DR

The site config references the docs plugin but Node cannot resolve it: either the package was never installed, or it is listed manually in plugins while preset-classic already bundles it. Install the package (or remove the redundant manual entry), then rebuild. The build passes because the plugin name now resolves to real code.

The error

Error: plugin not found: @docusaurus/plugin-content-docs
    at loadPlugin (node_modules/@docusaurus/core/lib/server/plugins/index.js)

Steps

1. Check whether it is installed: npm ls @docusaurus/plugin-content-docs.

Expected: either a version tree or an '(empty)' / not-found note.

1. If it is missing, install it: npm install @docusaurus/plugin-content-docs.

Expected: the package appears in package.json dependencies and node_modules.

1. If the site uses @docusaurus/preset-classic, do NOT also list the plugin in the plugins array of docusaurus.config.js - the preset already includes it. Remove the manual entry instead of installing.

Expected: the plugin is provided exactly once: by the preset or by the manual entry, not both.

1. Check the plugins array for typos in the package name.

Expected: the name matches the installed package exactly.

1. Rebuild: npm run build.

Expected: the plugin loads and the docs routes build with no plugin error.

Use this when

• the build fails naming @docusaurus/plugin-content-docs as not found
• a Docusaurus site scaffolded by hand rather than the CLI template
• the plugin was removed from package.json during a dependency cleanup

Not for this skill when

• 'broken markdown link' (content problem, the plugin loaded fine)
• 'MDX compilation failed' (a page does not parse)
• a plugin that loads but misbehaves (wrong options, not a resolution failure)

Variant phrasings

• docusaurus plugin-content-docs not found
• docusaurus Error plugin not found build
• docusaurus preset-classic plugin-content-docs duplicate
• @docusaurus/plugin-content-docs missing

Why it happens

Docusaurus resolves each entry in the config's plugins array as a Node module at startup. The docs plugin ships inside @docusaurus/preset-classic, which most templates use, so hand-edited configs often add a second manual entry or reference the plugin in a project that never installed it. Either way the resolver fails before any page builds, which is why the error names the plugin rather than a file.

Edge cases

• After changing plugins, delete the .docusaurus cache directory; stale plugin state there can survive a config fix.
• Version skew between the plugin and @docusaurus/core produces cryptic errors later in the build - keep all @docusaurus/* packages on the same version.
• The same 'plugin not found' shape applies to any community plugin; the diagnosis (npm ls, then install or de-duplicate) is identical.

Provenance

Resolved from the public thread: https://vectle.com/posts/pst_dP8eudKJtuQbI9UzUKfHWg