# Adding plug-ins via the registry

DITA-OT supports a plug-in registry that makes it easier to discover and install new plug-ins. The registry provides a searchable list of plug-ins at dita-ot.org/plugins.

In the past, installing plug-ins required you to either download a plug-in to your computer and provide the path to the plug-in archive (.zip file) or pass the URL of the plug-in distribution file to the dita command and let DITA-OT download the file. This required that you know the URL of the plug-in distribution package.

## Installing plug-ins from the registry

With the registry, you can now search the list of available plug-ins at dita-ot.org/plugins and install new plug-ins by name and optional version.

Search the registry for a plug-in and install it by providing the plug-in name to the dita command.

    dita --install=<plugin-name>

If the registry includes multiple versions of the same plug-in, you can specify the version to install as follows:

    dita --install=<plugin-name>@<plugin-version>

If the plug-in requires other plug-ins, those are also installed recursively.

For example, to revert PDF output to the legacy PDF2 layout that was the default in DITA-OT before 2.5, install the org.dita.pdf2.legacy plug-in as follows:

    dita --install=org.dita.pdf2.legacy

If a matching plug-in cannot be found, an error message will appear. Possible reasons for failure include:

- A plug-in with the specified name was not found in the registry
- A plug-in with the specified version was not found in the registry
- The specified plug-in version is not compatible with the installed DITA-OT version
- None of the available plug-in versions are compatible with the installed DITA-OT version

## Publishing plug-ins to the registry

The contents of the DITA Open Toolkit plug-in registry are stored in a Git repository at github.com/dita-ot/registry. New plug-ins or new versions can be added by sending a pull request that includes a single new plug-in entry in JavaScript Object Notation (JSON) format.

Note:
As for all other contributions to the project, pull requests to the registry must be signed off by passing the `--signoff` option to the git commit command to certify that you have the rights to submit this contribution. For more information on this process, see signing your work.

The version entries for each plug-in are stored in a file that is named after the plug-in ID as `<plugin-name>.json`. The file contains an array of entries with a pre-defined structure. You should have one entry for each supported version of the plug-in.

Table 1. Plug-in version entry structure
Key | Mandatory | Description
--- | --- | ---
`name` | yes | Plug-in name
`vers` | yes | Plug-in version in semantic versioning format
`deps` | yes | Array of dependency entries. The only mandatory plug-in dependency is `org.dita.base`, which defines the supported DITA-OT platform.
`url` | yes | Absolute URL to plug-in distribution file
`cksum` | no | SHA-256 hash of the plug-in distribution file
`description` | no | Description of the plug-in
`keywords` | no | Array of keywords
`homepage` | no | Plug-in homepage URL
`license` | no | License in SPDX format

Tip:
To calculate the SHA-256 checksum for the `cksum` key, use `shasum -a 256 <plugin-file>` on macOS or Linux. With Windows PowerShell, use `Get-FileHash <plugin-file> | Format-List`.

Table 2. Structure for dependency entries
Key | Mandatory | Description
--- | --- | ---
`name` | yes | Plug-in name
`req` | yes | Required plug-in version in semantic versioning format that may contain ranges.

Note:
Version numbers in the `vers` and `req` keys use the three-digit format specified by semantic versioning. An initial development release of a plug-in might start at version 0.1.0, and an initial production release at 1.0.0. If your plug-in requires DITA-OT 3.1 or later, set the `req` key to `>=3.1.0`. Using the greater-than sign allows your plug-in to work with compatible maintenance releases, such as 3.1.3. If the requirement is set to `=3.1.0`, the registry will only offer it for installation on that exact version.

## Sample plug-in entry file

The example below shows an entry for the `DocBook` plug-in. The complete file is available in the registry as org.dita.docbook.json.

    [
      {
        "name": "org.dita.docbook",
        "description": "Convert DITA to DocBook.",
        "keywords": ["DocBook"],
        "homepage": "https://github.com/dita-ot/org.dita.docbook/",
        "vers": "2.3.0",
        "license": "Apache-2.0",
        "deps": [
          {
            "name": "org.dita.base",
            "req": ">=2.3.0"
          }
        ],
        "url": "https://github.com/dita-ot/org.dita.docbook/archive/2.3.zip",
        "cksum": "eaf06b0dca8d942bd4152615e39ee8cfb73a624b96d70e10ab269ed6f8a13e21"
      }
    ]

## Maintaining multiple plug-in versions

When you have multiple versions of a plug-in, include an entry for each version, separated by a comma:

    [
      {
        "name": "org.example.myplugin",
         [...]
        "vers": "1.0.1",
         [...]
      },
      {
        "name": "org.example.myplugin",
         [...]
        "vers": "2.1.0",
         [...]
      }
    ]

Tip:
To publish a new version of your plug-in to the registry, add a new entry to the array in the existing plug-in entry file rather than overwriting an existing entry. This allows users to install the previous version of the plug-in if they are using an older version of DITA-OT.

## Adding custom registries

In addition to the main plug-in registry at dita-ot.org/plugins, you can create a registry of your own to store the custom plug-ins for your company or organization.

A registry is just a directory that contains JSON files like the one above; each JSON file represents one entry in the registry. To add a custom registry location, edit the config/configuration.properties file in the DITA-OT installation directory and add the URL for your custom registry directory to the `registry` key value, separating each entry with a space.

Tip:
Custom registry entries are a simple way to test your own plug-in entry file before submitting to a common registry.

## Testing with a custom registry

To test your plug-in entry with a custom registry:

1. Fork the plug-in registry, which creates a new repository under your GitHub username — for example, `https://github.com/USERNAME/registry.git`.
2. Create a new branch for your plug-in entry, and add the JSON file to the branch — for example, create org.example.newPlugin.json in the branch `addPlugin`.
3. As long as your repository is accessible, that branch now represents a working “custom registry” that can be added to the config/configuration.properties file. Edit the `registry` key and add the raw GitHub URL for the branch that contains the JSON file. With the example username and branch name above, you can add your registry with:

       registry=https://raw.githubusercontent.com/USERNAME/registry/addPlugin/ http://plugins.dita-ot.org/

4. You can now test the plug-in installation with:

       dita --install=org.example.newPlugin

5. Once you’ve confirmed that the entry works, you can submit a pull request to have your entry added to the common registry.