# Transformers
Transformers are a way to sanitize, transform and alter the data:
* going INTO a function (MCP, or Collection). Trigger: `onFunctionInput`.
* coming OUT a function (MCP, or Collection). Trigger: `onFunctionOutput`.
* being loaded from a resource. Trigger: `onResource`.

Transformers are defined outside the realm of sessions, and are triggered by hooks.

## Operators
* `parser`: (csv/json) if the input data is **plain text** parse the input data into a **structured output**.
* `jsonata`: apply a [JSONata](https://jsonata.org/) expression to the structured input (currently deprecated) 
* `jmesPath`: apply a [JMESPath](https://jmespath.org/) expression to the structured input
* `expr`: apply an [Go Expr](https://github.com/expr-lang/expr) expression to the structured input
* `code`: run a script against the input data, assuming the integrating application provides a scripting engine. The
  CLI supports a vanilla JavaScript runtime.

A single transformer can implement all the above operators and will be applied as a transformation chain top-down.

## YAML
This example sanitizes GitHub pull request data (MCP function):
```yaml
transformers:
  - name: cleanup_atlassian
    onFunctionOutput: search_pull_requests
    jsonata: |-
      items.{
        "title": title,
        "state": state,
        "url": html_url,
        "author": user.login
      }
```

This example loads a csv [resource](Resources.md) into memory, but first makes into a data structure so that the prompt can reference it:
```yaml
transformers:
  - name: csv1
    onResource: data/data2.csv
    parser: csv
    jmesPath: '[1:].{first_name: [0], last_name: [1]}'
sessions:
  parsed_content_into_memory:
    prompt: |-
      who was {{ (index .vars.data2 2).first_name }} {{ (index .vars.data2 2).last_name }}.
    resources:
      - identifier: data/data2.csv
        in: vars
        var: data2
```
## Go
Same as the YAML version, nothing special here.