error calling partial: the two things it usually means

The build stops in the middle of a template:

Error: error calling partial: partial "header.html" not found

or:

Error: error calling partial: runtime error: invalid memory address
       or nil pointer dereference

The messages look different, but the two common causes are straightforward.

“partial … not found”

Check the partial name and lookup path in this order:

1. The name has to match the file, extension included.

{{ partial "header.html" . }}   ← looks for header.html
{{ partial "nav/main.html" . }} ← looks for nav/main.html in a subfolder

The path is relative to the partials directory, not to the template calling it.

2. The file has to be in the partials directory.

Recent Hugo keeps partials in layouts/_partials/. Older projects use layouts/partials/. Both still work today, but don’t mix them in one project – pick the one your Hugo version generates and keep every partial there.

3. A theme’s partials are only found under the theme.

If you’re overriding a theme partial, mirror its path exactly in your own layouts/. themes/x/layouts/_partials/nav.html is overridden by layouts/_partials/nav.html – same relative path, or Hugo keeps using the theme’s.

The nil pointer: you forgot the dot

{{ partial "header.html" }}     ← no context
{{ partial "header.html" . }}   ← context passed

That trailing . is the page. Leave it out and the partial gets nothing – so the moment it reaches for .Title or .Params, it’s reaching into nothing, and Go panics.

You don’t have to pass the whole page. If a partial needs three specific values, hand it exactly those:

{{ partial "card.html" (dict "title" .Title "url" .RelPermalink "date" .Date) }}

Inside the partial, .title and .url refer to the dictionary keys. Passing explicit values also limits the partial’s dependencies.

Reading the error

Read the complete error to find the template path and line number:

Error: error calling partial: execute of template failed at
       <.Title>: nil pointer evaluating page.Page.Title
       in layouts/_partials/header.html:4:12

header.html:4:12 identifies line 4, column 12 inside the partial. Check the corresponding call site for missing context.

In HugoKit: Preflight reports missing partial context and partial names that do not match a file.