Copier JOLT

Copier JOLT is a JOLT-maintained fork of Copier for rendering and maintaining project templates.

Upstream credit: This project began as a fork of Copier.

Repository: https://github.com/landfair-biz/copier-jolt

Copier JOLT retains Copier's template rendering, answer management, Git-based template workflow, and update capabilities, while adding a more guided interactive prompting experience.

What is different in Copier JOLT?

In addition to the standard Copier workflow, this fork adds the following features for template authors:

Feature	What it adds
Prompt navigation	Let users review and revise previously entered interactive answers before generation continues.
Inline prompt formatting	Use bold text and prompt-toolkit colors inside help text and string defaults.
Non-blocking warnings	Give users contextual guidance without rejecting their answer. String warnings update while the user types.
Question pre-tasks	Run a trusted command before a question and use its output to build dynamic prompt choices.
Dynamic question groups	Repeat a set of related questions based on an earlier answer and save the results as a list of mappings.

These additions are opt-in: templates without the new settings continue to use the familiar Copier behavior.

Installation

Copier JOLT requires Python 3.10 or newer and Git 2.27 or newer.

Install the current version directly from this repository with your preferred Python tool:

pipx install git+https://github.com/landfair-biz/copier-jolt.git

uv tool install git+https://github.com/landfair-biz/copier-jolt.git

Or install it into an existing Python environment:

pip install git+https://github.com/landfair-biz/copier-jolt.git

The command-line program remains copier:

copier --help-all

Quick start

A template is a directory containing a copier.yml (or copier.yaml) configuration file and the files to render.

my-template/
├── copier.yml
├── {{ project_name }}/
│   └── README.md.jinja
└── {{ _copier_conf.answers_file }}.jinja

A minimal copier.yml:

project_name:
  type: str
  help: What is your project name?

module_name:
  type: str
  help: What is your Python module name?

A templated file, {{ project_name }}/README.md.jinja:

# {{ project_name }}

Python package: `{{ module_name }}`

Generate a project from a local template:

copier copy path/to/my-template path/to/new-project

Templates may also be Git URLs or shortcuts such as gh:organization/template. To use this fork itself as a template source, use:

copier copy https://github.com/landfair-biz/copier-jolt.git path/to/destination

You can also call Copier JOLT from Python:

from copier import run_copy

run_copy("path/to/my-template", "path/to/new-project")

JOLT prompt features

Add these settings to question dictionaries in copier.yml.

Review and edit answers

Set prompt_navigation: true at the top level of your template configuration to offer an answer-review step after the interactive questionnaire.

prompt_navigation: true

project_name:
  type: str
  help: Name of the new project

license:
  type: str
  choices:
    - MIT
    - Apache-2.0
    - Proprietary

After answering the prompts, Copier JOLT asks whether the user wants to review or edit answers. If they do, it shows the questions answered during that session. Choosing a question returns to that point in the questionnaire and clears the answers from that question onward so dependent questions can be answered again.

This is designed for interactive use. Non-interactive runs that provide --defaults, --data, or --data-file continue as usual.

Format help and default text

Use [bold]...[/bold] to emphasize text and [color=COLOR]...[/color] to apply a prompt-toolkit color. Formatting is supported in a question's help and in string default values.

service_name:
  type: str
  help: "Choose a [bold]unique[/bold] name. Use [color=ansiblue]lowercase letters and dashes[/color]."
  default: "[color=ansigreen]my-service[/color]"

The prompt displays the styled help text and a formatted default preview. The markup is presentation-only: accepting the default above saves my-service, never [color=ansigreen]my-service[/color].

Colors use prompt-toolkit color names. Common choices include ansiblue, ansigreen, ansiyellow, ansired, ansicyan, and ansimagenta.

Formatting can be combined:

project_slug:
  type: str
  help: "[bold][color=ansiyellow]Required:[/color][/bold] use a lowercase URL-safe slug."
  default: "[bold]sample-project[/bold]"

Keep markup well-formed by closing every [bold] and [color=...] tag. The feature only affects help and string defaults; it does not change the values rendered into generated files.

Give non-blocking warnings

Use warning when an input is allowed but merits attention. Like a validator, it is a Jinja template that renders an empty string when no warning applies. Unlike a validator, it never blocks the user from proceeding.

project_name:
  type: str
  help: Project name
  warning: >-
    {% if project_name | length < 5 %}
    Short names can be hard to discover later.
    {% endif %}

For string questions without choices, the warning appears in the prompt's bottom toolbar while the user types and disappears as soon as the condition is resolved. Choice prompts show the warning in the bottom toolbar for the highlighted option. In this example, the message clears once the name has five or more characters.

Warnings can guide users about conventions without forbidding exceptions:

database_url:
  type: str
  help: Database connection URL
  warning: >-
    {% if database_url.startswith('postgres://') %}
    Prefer the postgresql:// scheme for new connections.
    {% endif %}

Use validator for requirements that must prevent submission, such as an invalid project slug; use warning for advice and review cues. For non-string prompts or string prompts with choices, a warning is displayed after the answer is submitted.

Build choices from a command

A question can define pre_tasks: commands that run immediately before that question is displayed. Each task must have a name and a command. Its result becomes available to the question's templates at _pre_tasks.<name>.

The result exposes:

• stdout — complete standard output as text
• stderr — complete standard error as text
• lines — standard output split into newline-separated values

For example, list network interfaces and offer them as choices:

network_interface:
  type: str
  help: Select the interface this service should bind to.
  pre_tasks:
    - name: interfaces
      command: [sh, -c, "ls /sys/class/net"]
  choices: |
    {% for interface in _pre_tasks.interfaces.lines %}
    - {{ interface }}
    {% endfor %}

Use a pre-task to derive choices from a project tool as well:

package_manager:
  type: str
  pre_tasks:
    - name: available
      command: [sh, -c, "printf 'uv\npip\npoetry\n'"]
  choices: |
    {% for manager in _pre_tasks.available.lines %}
    - {{ manager }}
    {% endfor %}

Commands can be a shell-style string or an argument list. You can conditionally run a task with when:

deployment_region:
  type: str
  pre_tasks:
    - name: regions
      command: [sh, -c, "./scripts/list-regions"]
      when: "{{ cloud_provider == 'aws' }}"
  choices: |
    {% for region in _pre_tasks.regions.lines %}
    - {{ region }}
    {% endfor %}

Security: Pre-tasks execute commands with the same permissions as the person running Copier. Only use templates you trust. Pre-tasks use the same trusted-template approval flow as normal template tasks and are skipped when running with --skip-tasks.

Ask a dynamic group of questions

Use a dynamic question group when an earlier response determines how many similarly structured records you need. Define repeat with a value or Jinja expression that resolves to a non-negative integer, then define the fields for each entry in questions.

elasticsearch_node_count:
  type: int
  help: How many Elasticsearch nodes are in the cluster?

elasticsearch_nodes:
  repeat: "{{ elasticsearch_node_count }}"
  defaults:
    hostname: "es-{{ _repeat.number }}"
    ip_address: "10.0.0.{{ _repeat.number }}"
  questions:

    hostname:
      type: str
      help: "Hostname for node {{ _repeat.number }} of {{ _repeat.count }}"
    mac_address:
      type: str
      help: "MAC address for node {{ _repeat.number }}"
    ip_address:
      type: str
      help: "IP address for node {{ _repeat.number }}"

Use defaults for values shared by each entry, including templates that use _repeat. You can also provide a list of mappings in defaults when each entry needs distinct defaults. A nested question's own default remains available when a group default is not supplied. In interactive runs, an invalid default is shown so the user can correct it; --defaults still rejects invalid values.

For a count of 2, the answers file receives one list under elasticsearch_nodes:

elasticsearch_nodes:
  - hostname: es-1
    mac_address: "00:11:22:33:44:55"
    ip_address: 10.0.0.11
  - hostname: es-2
    mac_address: "00:11:22:33:44:66"
    ip_address: 10.0.0.12

Inside repeated prompts, _repeat.index is zero-based, _repeat.number is one-based, _repeat.count is the total number of records, and _repeat.group is the group name. The resulting list is available to files and later prompts as elasticsearch_nodes.

Validate repeated entries

Nested dynamic fields support validator and warning. During validation or warning rendering, _repeat.value contains the answer currently being evaluated and _repeat.entries contains the generated entries, so far. This prevents duplicate IP addresses while enforcing a 10.42.0.x range:

elasticsearch_nodes:
  repeat: "{{ elasticsearch_node_count }}"
  questions:
    ip_address:
      type: str
      validator: >-
        {% if not (_repeat.value | regex_search('^10\\.42\\.0\\.(?:[1-9]|[1-9][0-9]|1[0-9]{2}|2[0-4][0-9]|25[0-4])$')) %}
        Use an address in the 10.42.0.1–10.42.0.254 range.
        {% endif %}
        {% for node in _repeat.entries[:_repeat.index] %}
        {% if node.ip_address | default('') == _repeat.value %}
        This IP address is already assigned to an earlier node.
        {% endif %}
        {% endfor %}
      warning: >-
        {% if _repeat.value.endswith('.1') %}
        Addresses ending in .1 are often reserved for gateways.
        {% endif %}

Combining the features

The following example uses navigation, formatted guidance, a live warning, and dynamic choices together:

prompt_navigation: true

cloud_provider:
  type: str
  help: Choose where this service will run.
  choices:
    - AWS
    - Local

region:
  type: str
  help: "Select a [bold]deployment region[/bold]."
  pre_tasks:
    - name: regions
      command: [sh, -c, "./scripts/list-regions"]
      when: "{{ cloud_provider == 'AWS' }}"
  choices: |
    {% if cloud_provider == 'AWS' %}
    {% for region_name in _pre_tasks.regions.lines %}
    - {{ region_name }}
    {% endfor %}
    {% else %}
    - local
    {% endif %}

service_slug:
  type: str
  help: "Use [color=ansicyan]lowercase letters, digits, and dashes[/color]."
  default: "[color=ansigreen]my-service[/color]"
  validator: >-
    {% if not (service_slug | regex_search('^[a-z][a-z0-9-]+$')) %}
    Start with a lowercase letter; use only lowercase letters, digits, and dashes.
    {% endif %}
  warning: >-
    {% if service_slug | length < 8 %}
    A longer service slug is usually easier to identify in logs.
    {% endif %}

Here, invalid slugs are rejected by validator, short-but-valid slugs show an advisory warning, the available regions depend on the provider, and the final review permits corrections before rendering.

Core Copier capabilities

Copier JOLT continues to support the established Copier workflow:

• Render template variables in file contents, filenames, and directory names.
• Store answers in an answers file for repeatable generation and updates.
• Use local templates, Git repositories, Git URLs, and gh:/gl: shortcuts.
• Pass values non-interactively with --data or a data file.
• Recopy projects or update generated projects as their templates evolve.
• Use Jinja expressions, conditions, validation, choices, secrets, and tasks in template configuration.

For all command options, run:

copier --help-all

Contributing and license

Issues, feature requests, and contributions belong in the Copier JOLT repository.

Copier JOLT is distributed under the MIT License. See LICENSE for details.