tempo

A lightweight CLI for managing assets and scaffolding components in templ-based projects.

tempo is a lightweight CLI for managing assets and scaffolding components in templ-based projects. Inspired by the Italian word for "time", it streamlines CSS & JS workflows while preserving a smooth developer experience.

📖 Table of Contents

• ✨ Features
• 💡 Motivation
• 💻 Installation
• 🚀 Usage
• 🛠️ CLI Commands & Options
• ⚡ Using tempo sync as a Standalone Command
• ⚙️ Configuration
• 🏗️ Templates & Actions
• 🔌 Extending Tempo
• 🤝 Contributing
• 🆓 License

✨ Features

• Automated CSS & JS management – Keeps styles and scripts in separate files while seamlessly injecting them into .templ components.
• Structured asset workflow – Ensures a clean, maintainable approach to managing CSS and JS within templ projects.
• Fast, lightweight component scaffolding – Quickly generate components and variants with predefined templates and actions.
• Extensible templating system – Supports custom function providers (local or remote) to enhance tempo's capabilities.

💡 Motivation

While building a UI component library in Golang with templ, I deliberately chose to use plain CSS and vanilla JavaScript. This decision introduced two key challenges:

The Problem

1. Managing CSS & JS assets – While templ excels at Go/HTML templating, it lacks a structured approach for handling standalone styles and scripts. Although you can write CSS and JS directly within .templ files, this comes at the cost of losing native tooling benefits such as syntax highlighting, formatting, and autocompletion. As a result, maintaining styles and scripts efficiently while keeping them separate from .templ files required a better workflow.
2. Scaffolding new components – Every component followed the same folder structure, but manually copying files and folders was inefficient. I initially used Plop.js, but it required setting up a full Node.js project.

The Solution

tempo solves both problems natively in Go, eliminating the need for Node.js while providing a structured, opinionated workflow for component and asset management.

✨ Preserving the Developer Experience

With tempo, CSS and JS files remain untouched during development, allowing developers to continue using their preferred tools:

• Linters & formatters (e.g., Prettier, ESLint, Stylelint)
• IDE features like syntax highlighting, error detection, and inline code suggestions (e.g., in VSCode).
• Existing workflows remain intact—ensuring a familiar, efficient experience.

When you run tempo, CSS and JS files are injected into .templ components automatically, but the original source files remain unchanged. This approach preserves developer productivity while enabling seamless integration into templ-based projects.

💻 Installation

go install

Requires Go v1.23+

go install github.com/indaco/tempo@latest

Manually

Download the pre-compiled binaries from the releases page and place it in a directory available in your system's PATH.

🚀 Usage

To start using tempo, initialize your project and define your components. Below are the key steps:

1. Initialize tempo

tempo init

Generates a tempo.yaml configuration file. Customize it to fit your project. See the Configuration section for details.

2. Define a Component or Variant

tempo component define
tempo variant define

Generates templates for components/variants inside .tempo-files/templates/ along with an action JSON file inside .tempo-files/actions/. See the Templates & Actions section for details.

3. Create a Component

tempo component new --name button

Creates a new component:

• assets/button/ → Holds CSS and JS files.
• components/button/ → Contains .templ and .go file

4. Sync Assets with Components

tempo sync

Injects CSS & JS into .templ files using guard markers.

🔹 Example mapping:

assets/button/css/button.css          → components/button/css/button.templ
assets/button/css/variant/outline.css → components/button/css/variant/outline.templ

🛠️ CLI Commands & Options

NAME:
   tempo - A lightweight CLI for managing assets and scaffolding components in templ-based projects.

USAGE:
   tempo <subcommand> [options] [arguments]

VERSION:
   v0.1.0

DESCRIPTION:
   tempo simplifies asset management in templ-based projects, providing a seamless workflow for
   handling CSS and JS files. It automatically extracts and injects styles and scripts into .templ
   components while preserving the original source files, ensuring a smooth developer experience.
   Additionally, it offers a lightweight scaffolding system to quickly generate component and variant
   templates with predefined structures.

COMMANDS:
   init       Initialize a Tempo project
   component  Define component templates and generate instances from them
   variant    Define variant templates and generate instances from them
   register   Register is used to extend tempo
   sync       Process & sync asset files into templ components
   help       Shows a list of commands or help for one command

GLOBAL OPTIONS:
   --help, -h     show help
   --version, -v  print the version

init

Initialize a tempo project by generating a tempo.yaml configuration file. This file allows you to customize how components and assets are generated and managed.

For a full list of configuration options, See the Configuration section for details.

component

Define reusable component templates and generate instances from them.

Define a Component

tempo component define

Creates a scaffold for defining a UI component, including template files and an action JSON file.

These definitions are later used by tempo component new to generate real components.

Generate a Component

tempo component new --name button

Uses the templates and actions created with tempo component define to generate a real component inside assets/ and components/.

Example: Running tempo component new --name dropdown will generate:

• assets/dropdown/ (CSS & JS files)
• components/dropdown/ (with .templ and .go files)

variant

Define component variant templates and create instances based on them.

Define a Variant

tempo variant define

Creates a scaffold for defining a variant of an existing component (e.g., an outline button variant), including template files and an action JSON file.

These definitions are later used by tempo variant new to generate real component variants.

Generate a Variant

tempo variant new --name outline --component button

Uses the templates and actions created with tempo variant define to generate a real instance of a variant inside the corresponding component folder.

Example: Running tempo variant new --name outline --component button will generate:

• components/button/variant/outline.templ
• assets/button/css/variant/outline.css

register

Extend tempo with the register command.

tempo register -h

Register a function provider

Enhance tempo’s templating capabilities by adding custom function providers. You can register a provider from either a local Go module or a remote Git repository.

tempo register functions --name sprig --url https://github.com/indaco/tempo-provider-sprig.git

sync

Automatically sync CSS and JS assets with .templ components.

tempo sync

The sync command scans the input folder for CSS and JS files, then injects their content into the corresponding .templ files in the output folder:

• Extracts CSS and JS from source files.
• Injects them into .templ files inside sections marked by guard markers.
• Keeps components up to date without manual copying.

Whenever you update your CSS or JS files, simply run tempo sync to propagate the changes.

[!TIP] Live Reload: If you're using a live reload tool like air, templier, or watchexec, pass --summary none to reduce unnecessary output.

[!NOTE] Want to use tempo without scaffolding? Check out Using tempo sync as a Standalone Command.

⚡ Using tempo sync as a Standalone Command

The sync command can be used independently of the scaffolding flow (define, new, register). All it requires is:

• A valid tempo.yaml file.
• A project folder structure matching the paths defined in tempo.yaml.
• Guard markers in your .templ files to specify where assets should be injected.

This makes tempo sync a great option for developers who simply want to synchronize CSS and JS assets with their .templ files, without using the full scaffolding features.

💥 Use Cases for Standalone sync

• Already have components but want automated asset injection.
• Only need asset handling without using the full scaffolding flow.
• Maintain existing folder structures while benefiting from tempo’s synchronization features.

🛠️ Example Standalone Workflow

Start by creating a Go module using the go mod init command.

1. Initialize tempo.yaml:

   tempo init
   

2. Set up your folders:

   .
   ├── assets/
   │   └── button/
   │       └── button.css
   └── components/
       └── button/
           └── button.templ
   

3. Prepare .templ file with guard markers:

   package button
   
   var buttonCSSHandle = templ.NewOnceHandle()
   
   templ Button() {
     @buttonCSSHandle.Once() {
       <style type="text/css">
       /* [tempo] BEGIN - Do not edit! This section is auto-generated. */
       /* [tempo] END */
       </style>
   }
   

4. Run the sync command:

   tempo sync
   

5. Result:

CSS and JS are injected into the corresponding .templ files, replacing the content between the guard markers.

📋 Guard Markers Explained

tempo sync uses guard markers in .templ files to locate where CSS and JS should be injected.

By default, it looks for the following markers:

/* [tempo] BEGIN - Do not edit! This section is auto-generated. */
/* [tempo] END */

Only the text inside square brackets ([tempo]) can be customized in your tempo.yaml file under the templates.guard_marker setting.

[!IMPORTANT] If no guard markers are present, tempo sync will skip the file, ensuring only intended sections are updated.

⚙️ Configuration

# The root folder for Tempo files
tempo_root: .tempo-files

app:
  # The name of the Go module being worked on.
  go_module: <FROM_GO.MOD>

  # The Go package name where components will be organized and generated.
  go_package: components

  # The directory where asset files (CSS, JS) will be generated.
  assets_dir: assets

  # Indicates whether JavaScript is required for the component.
  # with_js: false

  # The name of the CSS layer to associate with component styles.
  # css_layer: components

processor:
  # Number of concurrent workers (numCPUs * 2).
  workers: 4

  # Summary format: long, compact, json, none.
  summary_format: compact

templates:
  # A text placeholder or sentinel used in template files to mark auto-generated content.
  guard_marker: tempo

  # File extensions used for template files.
  extensions:
    - .gotxt
    - .gotmpl
    - .tpl

Configuration Options

Project Structure

Application-Specific Settings

Files Processing Options

Templates Options

Function Provider Format

Each function provider entry follows this format:

templates:
  function_providers:
    - name: default
      type: path
      value: ./providers/default
    - name: custom
      type: url
      value: https://github.com/user/custom-provider.git

Fields

🛠️ Example Use Case

If your project follows a custom structure, you can update tempo.yaml like this:

app:
  go_module: myproject
  package: ui/components
  assets_dir: static/assets
  with_js: true
  css_layer: my-layer

This ensures:

• Assets are stored in static/assets
• Components are generated under ui/components
• JavaScript support is enabled
• CSS styles are associated with the my-layer layer

🏗️ Templates & Actions

📌 The tempo component define and tempo variant define commands generate:

• Templates stored in .tempo-files/templates/, using Go’s text/template.
• Actions defined in .tempo-files/actions/, specifying file and folder creation in JSON format.

Templates

Templates define the structure of components and variants. They use Go’s text/template engine along with custom template functions provided by Tempo.

📌 Default Template Functions

Tempo provides a set of built-in helper functions:

📌 Built-in Template Variables

Tempo automatically provides a set of predefined variables that can be used inside templates. These variables come from the configuration and CLI context during execution.

📌 Extending Template Functions

Tempo supports external function providers, allowing you to integrate additional helper functions into your templates.

See the full guide in Extending Tempo.

Actions

Actions define how templates should be processed. They are stored in .tempo-files/actions/ as JSON files.

Example component action file (component.json):

[
  {
    "item": "file",
    "templateFile": "component/templ/component.templ.gotxt",
    "path": "{{ .GoPackage }}/{{ .ComponentName | goPackageName }}/{{ .ComponentName | goPackageName }}.templ"
  },
  {
    "item": "file",
    "templateFile": "component/assets/css/base.css.gotxt",
    "path": "{{ .AssetsDir }}/{{ .ComponentName | goPackageName }}/css/base.css"
  },
  {
    "item": "folder",
    "source": "component/assets/css/themes",
    "destination": "{{ .AssetsDir }}/{{ .ComponentName | goPackageName }}/css/themes"
  }
]

Each object defines a templating action:

[!NOTE] When item is folder, all files inside the source folder will be processed and copied to the destination folder.

Variant actions (variant.json) follow the same structure but target a specific component’s variant subfolder.

🔌 Extending tempo

tempo provides two ways to extend how templates work:

1. Custom template variables — enrich templates with additional context using user_data.
2. Custom template functions — bring in new helpers via external function providers.

🔧 Adding Custom Template Variables

You can pass additional variables to your templates using the user_data section in the tempo.yaml config file. These variables are accessible inside templates using .UserData.

Example: tempo.yaml

# ....
templates:
  user_data:
    author: Jane Doe
    year: 2025
    config:
      option1: true
      option2: false

Basic Access (dot notation)

Author: {{ .UserData.author }}
Year: {{ .UserData.year }}

Nested Access

You can use either:

• index(built-in from text/template)
• lookup(provided by tempo, supports dot notation)

{{ index (index .UserData "config") "option1" }}
{{ lookup .UserData "config.option1" }}

📦 Using External Function Providers

You can add external function providers in two ways:

1. Via the tempo.yaml configuration file:

templates:
  function_providers:
    - name: sprig
      type: url
      value: https://github.com/indaco/tempo-provider-sprig.git

2. Via the CLI using the tempo register functions command:

• Register a GitHub repository provider:

  tempo register functions --name sprig --url https://github.com/indaco/tempo-provider-sprig.git
  

• Register a local provider from a directory:

  tempo register functions --name myprovider --path /path/to/myprovider_module
  

🛠 Implementing a Custom Template Function Provider

To create a custom function provider, implement the TemplateFuncProvider interface from the github.com/indaco/tempo-api.

See tempo api for full details.

Example: Creating a Custom Function Provider

package myprovider

import (
    "text/template"
    "github.com/indaco/tempo-api/templatefuncs"
)

// MyProvider implements the TemplateFuncProvider interface
type MyProvider struct{}

// GetFunctions returns a map of function names to implementations
func (p *MyProvider) GetFunctions() template.FuncMap {
    return template.FuncMap{
        "myFunc": func() string { return "Hello from myFunc!" },
    }
}

// Provider instance
var Provider templatefuncs.TemplateFuncProvider = &MyProvider{}

Once your provider is implemented:

• If published as a Git repository, register it using:

  tempo register functions --name myprovider --url https://github.com/user/myprovider_module.git
  

• If stored locally, register it using:

  tempo register functions --name myprovider --path /path/to/myprovider_module
  

📦 Available Function Providers

A pre-built function provider for Masterminds/sprig is available for convenience:

tempo register functions --name sprig --url https://github.com/indaco/tempo-provider-sprig.git

This allows you to access Sprig functions within Tempo templates.

🤝 Contributing

Contributions are welcome!

See the Contributing Guide for setting up the development tools.

🆓 License

This project is licensed under the MIT License - see the LICENSE file for details.