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, more alarmingly:

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

Two different messages, two different causes, and both are one-line fixes.

“partial … not found”

Hugo looked for the file and it wasn’t where it looks. Three things to check, in 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.

The message is scary and the cause is boring. It’s almost always the dot.

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 are then the keys of that dict – and the partial can’t accidentally depend on anything else, which is why it’s the better habit for anything reusable.

Reading the error

Hugo tells you which template blew up, and it’s worth reading past the first line:

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 – line 4, column 12. The panic happens inside the partial, but the bug is at the call site, in whatever template called it without the dot.

HugoKit’s preflight reads both of these out of the build log and offers a fix: it inserts the missing . into partial calls, and adds a missing .html where the name doesn’t match a file. Both land in layouts/ and are shown as a diff before anything is written. See Preflight.