---
id: jsonnet
title: Data Mapping with Jsonnet
---

Some modules like the
[OpenID Connect and OAuth2 Method](../concepts/credentials/openid-connect-oidc-oauth2.mdx)
support [Jsonnet](https://jsonnet.org), allowing you to easily write code that
modifies your identity's data and load it into ORY Kratos.

We highly recommend checking out the official
[learning Jsonnet tutorial](https://jsonnet.org/learning/tutorial.html).

## Formatting Jsonnet Code

Format Jsonnet code snippets using:

```shell script
$ kratos help jsonnet format

# e.g.:
$ kratos jsonnet format --write path/to/files/*.jsonnet
```

## Linting Jsonnet Code

Lint Jsonnet code snippets using:

```shell script
$ kratos help jsonnet lint

# e.g.:
$ kratos jsonnet lint path/to/files/*.jsonnet
```

The command will exit with an exit code of `1` and print all found lint errors
to stderr if the code snippet has lint issues.

## Testing Jsonnet Code

This is an anticipated future feature. For progress check out
[kratos#391](https://github.com/ory/kratos/issues/391).

## Tips & Tricks

The purpose of this section is to provide you with examples for common use
cases.

### Optionality

When you're unsure that a field will be set in the `claims` variable use the
following to make the trait field also optional:

```jsonnet
local claims = std.extVar('claims');

{
  identity: {
    traits: {
      email: claims.sub,
      [if "website" in claims then "website" else null]: claims.website,
    },
  },
}
```

### Defaults

Set defaults for the `claims` variable:

```jsonnet
local claims = {
 website: 'i am the default website value'
} + std.extVar('claims');

{
  identity: {
    traits: {
      website: claims.website
    }
  }
}
```

### Raising Errors

You can raise errors in the Jsonnet code. Keep in mind that these will be shown
as system errors, not validation errors, and that the user will end up at the
Error UI!

```jsonnet
local claims = std.extVar('claims');

if std.length(claims.sub) == 0 then
  error 'claim sub not set'
else
  {
    identity: {
      traits: {
        // ...
      },
    },
  }
```
