# Specifying Software Requirements

Often, tool descriptions will be written for a specific version of a software. To
make it easier for others to use your descriptions, you can include a
[`SoftwareRequirement`](https://w3id.org/cwl/CommandLineTool.html#SoftwareRequirement) field in the `hints` section.
This may also help to avoid confusion about which version of a tool the
description was written for.

```{literalinclude} /_includes/cwl/specifying-software-requirements/custom-types.cwl
:language: cwl
```

In this example, the software requirement being described is InterProScan
version 5.21-60.

```cwl
hints:
  SoftwareRequirement:
    packages:
      interproscan:
        specs: [ "https://identifiers.org/rrid/RRID:SCR_005829" ]
        version: [ "5.21-60" ]
```

Depending on your CWL runner, these hints may be used to check
that the required software is installed and available before the job is run. To enable
these checks with the reference implementation, use the [dependency resolvers configuration][dependencies].

As well as a version number, a unique resource identifier (URI) for the tool is
given in the form of an [RRID][rrid]. Resources with RRIDs can be looked up in the
[SciCrunch][scicrunch] registry, which provides a portal for finding, tracking,
and referring to scientific resources consistently. If you want to specify a
tool as a [`SoftwareRequirement`](https://w3id.org/cwl/CommandLineTool.html#SoftwareRequirement), search for the tool on SciCrunch and use the
RRID that it has been assigned in the registry. (Follow this [Adding a Resource Tutorial][scicrunch-add-tool] to add a tool to SciCrunch). You can use this RRID to refer
to the tool (via [identifiers.org][identifiers]) in the `specs` field of your
requirement description. Other good choices, in order of preference, are to
include the DOI for the main tool citation and the URL to the tool.


[rrid]: https://scicrunch.org/resources/about/resource
[scicrunch]: https://scicrunch.org/
[dependencies]: https://github.com/common-workflow-language/cwltool#leveraging-softwarerequirements-beta
[identifiers]: https://identifiers.org/
[scicrunch-add-tool]: https://scicrunch.org/page/tutorials/336