Ansible Read JSON File: lookup file Plugin & from_json (Guide)

How to Read a JSON file into a variable on the host with Ansible?

The JSON (JavaScript Object Notation) is an open standard file format used a lot for data interchange. I'm going to show you a live Playbook with some simple Ansible code. I'm Luca Berton, and welcome to today's episode of Ansible Pilot.

See also: Ansible lookup file Plugin: Read Local File Content into Variable (Guide)

Ansible reads a JSON file into a variable

• ansible.builtin.file - read file contents • from_json filter - converts the variable to JSON.

Let's dive deep into the Ansible lookup plugin file. Plugins are a way to expand the Ansible functionality. With lookup plugins specifically, you can load variables or templates with information from external sources. The full name is ansible.builtin.file; it's part of ansible-core and is included in all Ansible installations. The purpose of the file lookup plugin is to read file contents. The "from_json" is an Ansible-specific filter to convert the input to JSON. Let's combine the result of the file lookup plugin with the from_json filter for our use case.

Playbook

How to read the example.json JSON file, assign it to a variable and use it in your Ansible Playbook code.

code

• example.json

{
  "name": "John",
  "age": 30
}

• read_json.yml

---
- name: json read Playbook
  hosts: localhost
  vars:
    jsondata: "{{ lookup('file', 'example.json') | from_json }}"
  tasks:
    - name: Print variable
      ansible.builtin.debug:
        var: jsondata

execution

$ ansible-playbook read_json.yml 
[WARNING]: No inventory was parsed, only implicit localhost is available
[WARNING]: provided hosts list is empty, only localhost is available. Note that the
implicit localhost does not match 'all'
PLAY [json read Playbook] *******************************************************************
TASK [Gathering Facts] ******************************************************************
ok: [localhost]
TASK [Print variable] *******************************************************************
ok: [localhost] => {
    "jsondata": {
        "age": 30,
        "name": "John"
    }
}
PLAY RECAP ******************************************************************************
localhost                  : ok=2    changed=0    unreachable=0    failed=0    skipped=0    rescued=0    ignored=0

idempotency

$ ansible-playbook read_json.yml 
[WARNING]: No inventory was parsed, only implicit localhost is available
[WARNING]: provided hosts list is empty, only localhost is available. Note that the
implicit localhost does not match 'all'
PLAY [json read Playbook] *******************************************************************
TASK [Gathering Facts] ******************************************************************
ok: [localhost]
TASK [Print variable] *******************************************************************
ok: [localhost] => {
    "jsondata": {
        "age": 30,
        "name": "John"
    }
}
PLAY RECAP ******************************************************************************
localhost                  : ok=2    changed=0    unreachable=0    failed=0    skipped=0    rescued=0    ignored=0

code with ❤️ in GitHub

Conclusion

Now you know how to read a JSON file into a variable on the host with Ansible.

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

Read Local JSON File

- name: Load config
  set_fact:
    config: "{{ lookup('file', 'files/config.json') | from_json }}"
- debug:
    msg: "DB host: {{ config.database.host }}, port: {{ config.database.port }}"

Read JSON Relative to Playbook

- set_fact:
    settings: "{{ lookup('file', playbook_dir + '/settings.json') | from_json }}"

See also: Creating a Custom Ansible Lookup Plugin in Python for Reading a File

Read Remote JSON File

- name: Slurp remote JSON
  ansible.builtin.slurp:
    src: /etc/myapp/config.json
  register: remote_file
- name: Parse it
  set_fact:
    remote_config: "{{ remote_file.content | b64decode | from_json }}"
- debug:
    msg: "App mode: {{ remote_config.mode }}"

Read JSON from URL

- name: Fetch JSON API
  ansible.builtin.uri:
    url: https://api.example.com/config
    return_content: true
  register: api_response
- set_fact:
    api_data: "{{ api_response.json }}"  # Auto-parsed
    # OR: "{{ api_response.content | from_json }}"

Use JSON Data in Tasks

- vars:
    packages: "{{ lookup('file', 'packages.json') | from_json }}"
  # packages.json: {"install": ["nginx", "curl", "git"]}
  ansible.builtin.package:
    name: "{{ packages.install }}"
    state: present
  become: true

Load Multiple JSON Files

- name: Load all config files
  set_fact:
    "config_{{ item | basename | splitext | first }}": "{{ lookup('file', item) | from_json }}"
  loop: "{{ lookup('fileglob', 'configs/*.json', wantlist=True) }}"

Modify and Write Back

- set_fact:
    config: "{{ lookup('file', 'config.json') | from_json }}"
- set_fact:
    updated: "{{ config | combine({'version': '2.0', 'updated': true}) }}"
- ansible.builtin.copy:
    content: "{{ updated | to_nice_json }}"
    dest: /etc/myapp/config.json
  become: true

Include Variables from JSON

# Alternative: include_vars (auto-detects format)
- name: Load JSON as variables
  ansible.builtin.include_vars:
    file: settings.json
    name: settings

FAQ

file lookup vs include_vars — which should I use?

| Method | Scope | When to Use | |--------|-------|-------------| | lookup('file') | from_json | Set fact | Need to transform data | | include_vars | Load as variables | Direct variable usage |

What if the JSON file doesn't exist?

- set_fact:
    config: "{{ lookup('file', 'config.json', errors='ignore') | default('{}') | from_json }}"

Can I read JSON from a Jinja2 template?

Yes:

{% set config = lookup('file', 'config.json') | from_json %}
{{ config.server.host }}

Read Local JSON File

- set_fact:
    config: "{{ lookup('file', 'config.json') | from_json }}"
- debug:
    msg: "DB: {{ config.database.host }}:{{ config.database.port }}"

Read Remote JSON File

- slurp:
    src: /etc/myapp/config.json
  register: remote_file
- set_fact:
    config: "{{ remote_file.content | b64decode | from_json }}"
- debug:
    msg: "App version: {{ config.version }}"

Include Variables from JSON

# vars/config.json
# {"db_host": "localhost", "db_port": 5432, "debug": true}
- hosts: all
  vars:
    config: "{{ lookup('file', 'vars/config.json') | from_json }}"
  tasks:
    - debug: msg="{{ config.db_host }}"

Read and Filter

- set_fact:
    all_servers: "{{ lookup('file', 'servers.json') | from_json }}"
- set_fact:
    prod_servers: "{{ all_servers | selectattr('env', 'eq', 'production') | list }}"
    server_names: "{{ all_servers | map(attribute='name') | list }}"

Read Multiple JSON Files

- set_fact:
    db_config: "{{ lookup('file', 'db.json') | from_json }}"
    app_config: "{{ lookup('file', 'app.json') | from_json }}"
    merged: "{{ (lookup('file', 'defaults.json') | from_json) | combine(lookup('file', 'overrides.json') | from_json) }}"

Conditional Based on JSON

- set_fact:
    features: "{{ lookup('file', 'features.json') | from_json }}"
- name: Enable caching
  template:
    src: cache.conf.j2
    dest: /etc/myapp/cache.conf
  when: features.caching.enabled
- name: Configure monitoring
  template:
    src: monitoring.conf.j2
    dest: /etc/myapp/monitoring.conf
  when: features.monitoring.enabled

Dynamic Inventory from JSON

# hosts.json
# {"webservers": ["web1", "web2"], "dbservers": ["db1"]}
- set_fact:
    host_data: "{{ lookup('file', 'hosts.json') | from_json }}"
- debug:
    msg: "Web servers: {{ host_data.webservers | join(', ') }}"

Error Handling

# File might not exist
- set_fact:
    config: "{{ lookup('file', 'optional.json', errors='ignore') | default('{}') | from_json }}"
# With stat check
- stat: { path: files/config.json }
  register: config_file
  delegate_to: localhost
- set_fact:
    config: "{{ lookup('file', 'config.json') | from_json }}"
  when: config_file.stat.exists

lookup('file') vs include_vars

| Method | Source | Format | Scope | |--------|--------|--------|-------| | lookup('file') \| from_json | Controller | JSON | set_fact/vars | | include_vars | Controller | YAML/JSON | Play vars | | slurp \| from_json | Remote | JSON | set_fact | | uri \| .json | HTTP | JSON | register |

# include_vars works directly with JSON
- include_vars:
    file: config.json
    name: config

FAQ

lookup('file') vs slurp?

lookup('file') reads from the controller machine. slurp reads from the remote host. Use lookup for local config files, slurp for remote files.

Can I write back to a JSON file?

- copy:
    content: "{{ modified_config | to_nice_json }}"
    dest: files/config.json
  delegate_to: localhost

What if the JSON is invalid?

from_json will fail with a parse error. Validate your JSON files before using them.

Related Articles

• Jinja2 filters in Ansible templates • Ansible inventory groups and variables • Ansible JSON Conversion Guide • attribute management via ansible.builtin.file