Ansible to_yaml & to_nice_yaml Filters: Format Data as YAML (Guide)

The to_nice_yaml and to_yaml filters convert Ansible variables into YAML-formatted strings. They're essential for generating configuration files and debugging complex data structures.

to_yaml: Compact YAML

- name: Convert to compact YAML
  ansible.builtin.debug:
    msg: "{{ my_dict | to_yaml }}"

Output: {key1: value1, key2: value2}

See also: Ansible from_json & to_json Filters: Parse & Convert JSON (Guide)

to_nice_yaml: Human-Readable YAML

- name: Convert to readable YAML
  ansible.builtin.debug:
    msg: "{{ my_dict | to_nice_yaml }}"

Output:

key1: value1
key2: value2

Control Indentation

- name: Custom indent
  ansible.builtin.debug:
    msg: "{{ complex_data | to_nice_yaml(indent=4) }}"

See also: Ansible map Filter: Extract Attributes from Lists (Complete Guide)

Generate Configuration Files

- name: Write YAML config file
  ansible.builtin.copy:
    content: "{{ app_config | to_nice_yaml }}"
    dest: /etc/myapp/config.yml
    mode: '0644'

With a header comment

- name: Write config with header
  ansible.builtin.copy:
    content: |
      # Auto-generated by Ansible - DO NOT EDIT
      # Generated on {{ ansible_date_time.iso8601 }}
      {{ app_config | to_nice_yaml }}
    dest: /etc/myapp/config.yml

Practical Examples

Generate Docker Compose file

- name: Define compose config
  ansible.builtin.set_fact:
    compose_config:
      version: "3.8"
      services:
        web:
          image: "nginx:latest"
          ports:
            - "80:80"
          volumes:
            - "./html:/usr/share/nginx/html"
- name: Write docker-compose.yml
  ansible.builtin.copy:
    content: "{{ compose_config | to_nice_yaml }}"
    dest: /opt/app/docker-compose.yml

Debug complex variables

- name: Pretty-print all host facts
  ansible.builtin.debug:
    msg: "{{ ansible_mounts | to_nice_yaml }}"

Generate Kubernetes manifests

- name: Create K8s deployment
  ansible.builtin.copy:
    content: "{{ k8s_deployment | to_nice_yaml }}"
    dest: "/opt/k8s/deployment-{{ app_name }}.yml"

See also: Ansible map vs selectattr vs json_query: Filter Data the Right Way

to_nice_yaml vs to_yaml vs to_json

| Filter | Format | Human Readable | Use Case | |--------|--------|---------------|----------| | to_yaml | Compact YAML | No | Inline values | | to_nice_yaml | Indented YAML | Yes | Config files | | to_json | Compact JSON | No | API payloads | | to_nice_json | Indented JSON | Yes | JSON config files |

Handle Special Characters

# to_nice_yaml handles quoting automatically
- set_fact:
    config:
      password: "p@ss:word{special}"
      path: "/opt/my app/config"
- copy:
    content: "{{ config | to_nice_yaml }}"
    dest: /tmp/config.yml
# Output properly quotes strings with special characters

Width Control

# Prevent line wrapping for long strings
- debug:
    msg: "{{ data | to_nice_yaml(width=1000) }}"

FAQ

Why does to_nice_yaml add quotes around some values?

YAML has special characters (:, #, {, etc.). The filter adds quotes when values contain characters that could be misinterpreted.

Can I control the YAML version output?

The filter uses PyYAML defaults (YAML 1.1). For YAML 1.2 compliance, post-process the output or use custom Jinja2 filters.

How do I handle boolean values?

PyYAML may represent booleans as true/false. If you need yes/no or True/False, convert with string filters before serialization.

Basic Usage

- vars:
    config:
      server:
        host: 0.0.0.0
        port: 8080
      database:
        host: db.example.com
        port: 5432
        name: myapp
  debug:
    msg: "{{ config | to_nice_yaml }}"

Output:

database:
  host: db.example.com
  name: myapp
  port: 5432
server:
  host: 0.0.0.0
  port: 8080

Control Indentation

- debug:
    msg: "{{ config | to_nice_yaml(indent=4) }}"

Write YAML Config Files

- name: Generate app config
  ansible.builtin.copy:
    content: "{{ app_config | to_nice_yaml }}"
    dest: /etc/myapp/config.yml
    mode: '0644'
  become: true

to_yaml vs to_nice_yaml

- vars:
    data: { a: 1, b: [1, 2, 3] }
  debug:
    msg:
      - "Compact: {{ data | to_yaml }}"
      # {a: 1, b: [1, 2, 3]}
      - "Nice: {{ data | to_nice_yaml }}"
      # a: 1
      # b:
      # - 1
      # - 2
      # - 3

YAML Filters Reference

| Filter | Output | |--------|--------| | to_yaml | Compact single-line YAML | | to_nice_yaml | Human-readable indented YAML | | from_yaml | Parse YAML string to data | | to_json | Compact JSON | | to_nice_json | Pretty-printed JSON |

Generate Kubernetes Manifests

- vars:
    deployment:
      apiVersion: apps/v1
      kind: Deployment
      metadata:
        name: myapp
        labels:
          app: myapp
      spec:
        replicas: 3
        selector:
          matchLabels:
            app: myapp
  ansible.builtin.copy:
    content: "{{ deployment | to_nice_yaml }}"
    dest: /opt/k8s/deployment.yml

In Templates

# config.yml.j2
---
{{ app_settings | to_nice_yaml }}

FAQ

Why does to_nice_yaml add quotes around some strings?

YAML auto-quotes values that look like booleans (yes, no, true), numbers, or contain special characters. This is correct YAML behavior.

How do I prevent sorting keys?

As of Ansible 2.14+, keys maintain insertion order by default in Python 3.7+.

Can I use to_nice_yaml with Ansible Vault encrypted values?

No — encrypted values must stay as !vault tagged strings. Use to_nice_yaml only for unencrypted data.

Basic Usage

- vars:
    config:
      database:
        host: db.internal
        port: 5432
      cache:
        enabled: true
        ttl: 3600
  debug:
    msg: "{{ config | to_nice_yaml }}"

Output:

cache:
  enabled: true
  ttl: 3600
database:
  host: db.internal
  port: 5432

to_yaml vs to_nice_yaml

- debug:
    msg: "{{ config | to_yaml }}"
    # Compact: {cache: {enabled: true, ttl: 3600}, database: {host: db.internal, port: 5432}}
- debug:
    msg: "{{ config | to_nice_yaml }}"
    # Human-readable with proper indentation

Control Indentation

- debug:
    msg: "{{ config | to_nice_yaml(indent=4) }}"
# With custom width (line wrap)
- debug:
    msg: "{{ config | to_nice_yaml(indent=2, width=120) }}"

Write YAML to File

- copy:
    content: "{{ app_config | to_nice_yaml }}"
    dest: /etc/myapp/config.yml
  become: true
# With header comment
- copy:
    content: |
      # Managed by Ansible - DO NOT EDIT
      {{ app_config | to_nice_yaml }}
    dest: /etc/myapp/config.yml

Generate Config Files

- vars:
    nginx_config:
      worker_processes: auto
      events:
        worker_connections: 1024
      http:
        sendfile: true
        keepalive_timeout: 65
        gzip: true
  copy:
    content: "{{ nginx_config | to_nice_yaml }}"
    dest: /opt/myapp/nginx-config.yml

from_yaml + to_nice_yaml (Reformat)

# Read messy YAML, write clean YAML
- slurp: { src: /etc/myapp/config.yml }
  register: raw
- copy:
    content: "{{ raw.content | b64decode | from_yaml | to_nice_yaml }}"
    dest: /etc/myapp/config.yml

In Templates

{# config.yml.j2 #}
# Auto-generated by Ansible
{{ config_data | to_nice_yaml }}

Combine and Output

- vars:
    defaults:
      log_level: info
      port: 8080
    overrides:
      log_level: debug
  set_fact:
    final: "{{ defaults | combine(overrides) }}"
- copy:
    content: "{{ final | to_nice_yaml }}"
    dest: /etc/myapp/config.yml

YAML Filter Reference

| Filter | Output | |--------|--------| | to_yaml | Compact single-line YAML | | to_nice_yaml | Formatted multi-line YAML | | to_nice_yaml(indent=4) | Custom indentation | | from_yaml | Parse YAML string to object | | to_json | Compact JSON | | to_nice_json | Formatted JSON |

FAQ

Why does to_nice_yaml sort keys?

YAML dumper sorts keys alphabetically by default. This is normal and doesn't affect functionality.

How do I preserve key order?

You can't with to_nice_yaml — it uses Python's YAML dumper which sorts keys. Use template with Jinja2 for exact control.

Strings with special characters?

to_nice_yaml automatically quotes strings that contain YAML special characters (:, #, {, etc.).

Related Articles

• rendering Jinja2 templates with Ansible • Ansible JSON Conversion Guide • container lifecycle with Ansible • argv form of Ansible command • Nginx deployment with Ansible