Hugo Template Development Skill

Purpose

This skill enforces proper Hugo template development practices, including mandatory runtime testing to catch errors that static builds miss.

Critical Testing Requirement

Hugo's npx hugo --quiet only validates template syntax, not runtime execution.

Template errors like accessing undefined fields, nil values, or incorrect type assertions only appear when Hugo actually renders pages. You MUST test templates by running the server.

Mandatory Testing Protocol

For ANY Hugo Template Change

After modifying files in layouts/, layouts/partials/, or layouts/shortcodes/:

Step 1: Start Hugo server and capture output

npx hugo server --port 1315 2>&1 | head -50

Success criteria:

• No error calling partial messages
• No can't evaluate field errors
• No template: ... failed messages
• Server shows "Web Server is available at http://localhost:1315/"

If errors appear: Fix the template and repeat Step 1 before proceeding.

Step 2: Verify the page renders

curl -s -o /dev/null -w "%{http_code}" http://localhost:1315/PATH/TO/PAGE/

Expected: HTTP 200 status code

Step 3: Browser testing (if MCP browser tools available)

If mcp__claude-in-chrome__* tools are available, use them for visual inspection:

# Navigate and screenshot
mcp__claude-in-chrome__navigate({ url: "http://localhost:1315/PATH/", tabId: ... })
mcp__claude-in-chrome__computer({ action: "screenshot", tabId: ... })

# Check for JavaScript errors
mcp__claude-in-chrome__read_console_messages({ tabId: ..., onlyErrors: true })

This catches runtime JavaScript errors that template changes may introduce.

Step 4: Stop the test server

pkill -f "hugo server --port 1315"

Quick Test Command

Use this one-liner to test and get immediate feedback:

timeout 15 npx hugo server --port 1315 2>&1 | grep -E "(error|Error|ERROR|fail|FAIL)" | head -20; pkill -f "hugo server --port 1315" 2>/dev/null

If output is empty, no errors were detected.

Common Hugo Template Errors

1. Accessing Hyphenated Keys

Wrong:

{{ .Site.Data.article-data.influxdb }}

Correct:

{{ index .Site.Data "article-data" "influxdb" }}

2. Nil Field Access

Wrong:

{{ range $articles }}
  {{ .path }}  {{/* Fails if item is nil or wrong type */}}
{{ end }}

Correct:

{{ range $articles }}
  {{ if . }}
    {{ with index . "path" }}
      {{ . }}
    {{ end }}
  {{ end }}
{{ end }}

3. Type Assertion on Interface{}

Wrong:

{{ range $data }}
  {{ .fields.menuName }}
{{ end }}

Correct:

{{ range $data }}
  {{ if isset . "fields" }}
    {{ $fields := index . "fields" }}
    {{ if isset $fields "menuName" }}
      {{ index $fields "menuName" }}
    {{ end }}
  {{ end }}
{{ end }}

4. Empty Map vs Nil Check

Problem: Hugo's {{ if . }} passes for empty maps {}:

{{/* This doesn't catch empty maps */}}
{{ if $data }}
  {{ .field }}  {{/* Still fails if $data is {} */}}
{{ end }}

Solution: Check for specific keys:

{{ if and $data (isset $data "field") }}
  {{ index $data "field" }}
{{ end }}

Hugo Data Access Patterns

Safe Nested Access

{{/* Build up access with nil checks at each level */}}
{{ $articleDataRoot := index .Site.Data "article-data" }}
{{ if $articleDataRoot }}
  {{ $influxdbData := index $articleDataRoot "influxdb" }}
  {{ if $influxdbData }}
    {{ $productData := index $influxdbData $dataKey }}
    {{ if $productData }}
      {{ with $productData.articles }}
        {{/* Safe to use . here */}}
      {{ end }}
    {{ end }}
  {{ end }}
{{ end }}

Iterating Over Data Safely

{{ range $idx, $item := $articles }}
  {{/* Declare variables with defaults */}}
  {{ $path := "" }}
  {{ $name := "" }}

  {{/* Safely extract values */}}
  {{ if isset $item "path" }}
    {{ $path = index $item "path" }}
  {{ end }}

  {{ if $path }}
    {{/* Now safe to use $path */}}
  {{ end }}
{{ end }}

File Organization

Layouts Directory Structure

layouts/
├── _default/           # Default templates
├── partials/           # Reusable template fragments
│   └── api/            # API-specific partials
├── shortcodes/         # Content shortcodes
└── TYPE/               # Type-specific templates (api/, etc.)
    └── single.html     # Single page template

Partial Naming

• Use descriptive names: api/sidebar-nav.html, not nav.html
• Group related partials in subdirectories
• Include comments at the top describing purpose and required context

Separation of Concerns: Templates vs TypeScript

Principle: Hugo templates handle structure and data binding. TypeScript handles behavior and interactivity.

What Goes Where

Concern	Location	Example
HTML structure	layouts/**/*.html	Navigation markup, tab containers
Data binding	layouts/**/*.html	{{ .Title }}, {{ range .Data }}
Static styling	assets/styles/**/*.scss	Layout, colors, typography
User interaction	assets/js/components/*.ts	Click handlers, scroll behavior
State management	assets/js/components/*.ts	Active tabs, collapsed sections
DOM manipulation	assets/js/components/*.ts	Show/hide, class toggling

Anti-Pattern: Inline JavaScript in Templates

Wrong - JavaScript mixed with template:

{{/* DON'T DO THIS */}}
<nav class="api-nav">
  {{ range $articles }}
    <button onclick="toggleSection('{{ .id }}')">{{ .name }}</button>
  {{ end }}
</nav>

<script>
function toggleSection(id) {
  document.getElementById(id).classList.toggle('is-open');
}
</script>

Correct - Clean separation:

Template (layouts/partials/api/sidebar-nav.html):

<nav class="api-nav" data-component="api-nav">
  {{ range $articles }}
    <button class="api-nav-group-header" aria-expanded="false">
      {{ .name }}
    </button>
    <ul class="api-nav-group-items">
      {{/* items */}}
    </ul>
  {{ end }}
</nav>

TypeScript (assets/js/components/api-nav.ts):

interface ApiNavOptions {
  component: HTMLElement;
}

export default function initApiNav({ component }: ApiNavOptions): void {
  const headers = component.querySelectorAll('.api-nav-group-header');

  headers.forEach((header) => {
    header.addEventListener('click', () => {
      const isOpen = header.classList.toggle('is-open');
      header.setAttribute('aria-expanded', String(isOpen));
      header.nextElementSibling?.classList.toggle('is-open', isOpen);
    });
  });
}

Register in main.js:

import initApiNav from './components/api-nav.js';

const componentRegistry = {
  'api-nav': initApiNav,
  // ... other components
};

Data Passing Pattern

Pass Hugo data to TypeScript via data-* attributes:

Template:

<div
  data-component="api-toc"
  data-headings="{{ .headings | jsonify | safeHTMLAttr }}"
  data-scroll-offset="80"
>
</div>

TypeScript:

interface TocOptions {
  component: HTMLElement;
}

interface TocData {
  headings: string[];
  scrollOffset: number;
}

function parseData(component: HTMLElement): TocData {
  const headingsRaw = component.dataset.headings;
  const headings = headingsRaw ? JSON.parse(headingsRaw) : [];
  const scrollOffset = parseInt(component.dataset.scrollOffset || '0', 10);

  return { headings, scrollOffset };
}

export default function initApiToc({ component }: TocOptions): void {
  const data = parseData(component);
  // Use data.headings and data.scrollOffset
}

Minimal Inline Scripts (Exception)

The only acceptable inline scripts are minimal initialization that MUST run before component registration:

{{/* Acceptable: Critical path, no logic, runs immediately */}}
<script>
  document.documentElement.dataset.theme =
    localStorage.getItem('theme') || 'light';
</script>

Everything else belongs in assets/js/.

TypeScript Component Checklist

When creating a new interactive feature:

1. Create TypeScript file in assets/js/components/
2. Define interface for component options
3. Export default initializer function
4. Register in main.js componentRegistry
5. Add data-component attribute to HTML element
6. Pass data via data-* attributes (not inline JS)
7. NO inline <script> tags in templates

Debugging Templates

Enable Verbose Mode

npx hugo server --port 1315 --verbose 2>&1 | head -100

Print Variables for Debugging

{{/* Temporary debugging - REMOVE before committing */}}
<pre>{{ printf "%#v" $myVariable }}</pre>

Check Data File Loading

# Verify data files exist and are valid YAML
cat data/article-data/influxdb/influxdb3-core/articles.yml | head -20

Integration with CI/CD

Pre-commit Hook (Recommended)

Add to .lefthook.yml or pre-commit configuration:

pre-commit:
  commands:
    hugo-template-test:
      glob: "layouts/**/*.html"
      run: |
        timeout 20 npx hugo server --port 1315 2>&1 | grep -E "error|Error" && exit 1 || exit 0
        pkill -f "hugo server --port 1315" 2>/dev/null

GitHub Actions Workflow

- name: Test Hugo templates
  run: |
    npx hugo server --port 1315 &
    sleep 10
    curl -f http://localhost:1315/ || exit 1
    pkill -f hugo

Quick Reference

Action	Command
Test templates (runtime)	npx hugo server --port 1315 2>&1 | head -50
Build only (insufficient)	npx hugo --quiet
Check specific page	curl -s -o /dev/null -w "%{http_code}" http://localhost:1315/path/
Stop test server	pkill -f "hugo server --port 1315"
Debug data access	<pre>{{ printf "%#v" $var }}</pre>

Remember

1. Never trust npx hugo --quiet alone - it only checks syntax
2. Always run the server to test template changes
3. Check error output first before declaring success
4. Use isset and index for safe data access
5. Hyphenated keys require index function - dot notation fails

Related Skills

• cypress-e2e-testing - For E2E testing of UI components and pages
• docs-cli-workflow - For creating/editing documentation content
• ts-component-dev (agent) - TypeScript component behavior and interactivity
• ui-testing (agent) - Cypress E2E testing for UI components