Power Functions

Power Functions allow you to extend WeTransform by integrating your own custom logic directly into the transformation process.

Setting Up a Power Function

Creating and using a Power Function involves a few simple steps in the WeTransform interface.

Step 1: Define the Function

Navigate to the Integrations section and create a new Power Function. Give it a unique internal name, a description, and define the arguments it will receive.

• Name: Used in the rule editor (e.g., translate_text).
• Arguments: Define what data your server needs.

Step 2: Configure the Request

Choose how WeTransform calls your function. In Fetch mode, describe the HTTP request WeTransform executes against your API, once per row. In Callback mode, provide the Callback URL where WeTransform will send the trigger, plus a secret key for HMAC verification.

You can set custom timeouts for execution (up to 60 mins) and cache duration.

Step 3: Add to Rules

Once created, your function appears in the Rule Editor under the "Power Function" category. Select it and map your attributes to the function arguments.

Step 4: Monitor Execution

When a transformation runs, the columns affected by Power Functions will show a "pending" status. You can track progress in real-time on the Finalize page.

Execution Modes

A Power Function runs in one of two modes, selected when you configure the request.

Fetch Mode

In Fetch mode, you describe an HTTP request once, and WeTransform executes it once per row during the transformation, replacing placeholders with each row's values. There is nothing to implement on your side: if your API already exists, you are done.

The Request Template

Configure the method (GET, POST, PUT, PATCH or DELETE), URL, headers and body of the request. The URL, header values and body accept placeholders that are substituted for every row.

GET https://erp.acme.com/api/v1/products/{sku}/price?country={country}
Authorization: Bearer {token}

Picking the Outcome

The outcome — what lands in the cell — is read directly from the response. When the response is JSON, you can select the part you want with a path (e.g. price.amount). The editor's Test button runs the request once with sample values and lets you click the exact value in the response.

{
  "product": { "sku": "BRK-220", "label": "Brake kit 220 mm" },
  "price": { "amount": 129.95, "currency": "EUR" },
  "updated_at": "2026-07-01T06:12:00Z"
}

• No path set: the whole response body becomes the outcome.
• Response is not JSON: there is nothing to pick — the whole body is the outcome.

Performance & Caching

• Rows with identical argument values share a single call.
• Outcomes are cached for the configured cache duration and reused on later runs.
• The call timeout (1–60 seconds) applies to each individual request.

Try It Live: The Meow Demo Endpoint

Want to see Fetch mode work before wiring up your own API? We host a public, no-authentication demo endpoint — meow-as-a-service — that you can point a Fetch power function at right away. It takes any value and hands back a randomized cat meow in one of 26 languages.

GET https://api.wetransform.com/en/documentation/power-functions/meow?text={value}

Define a single argument named value and reference it as {value} in the URL above. Each row's cell value is sent as text, echoed back, and prefixed to the generated meow.

{
  "input": "Bonjour",
  "meow": "Bonjour miaou!!! MIAOU!!!",
  "language": "French",
  "lang_code": "fr",
  "style": "excited",
  "loudness": 7
}

Callback Mode: The Workflow

In Callback mode, Power Functions are asynchronous. This means that when a transformation starts, WeTransform sends a notification (a trigger) to your app, and your app works in the background to process the data.

1. The TRIGGER Call

When a user runs a transformation that includes your Power Function (in Callback mode), WeTransform sends a POST request to your callback URL.

{
  "function_name": "My Custom Function",
  "customer": { "customer_id": "...", "name": "John Doe" },
  "transformation": { "transformation_id": "...", "template_handle": "inventory" },
  "endpoints": {
    "fetch": "https://api.wetransform.com/power-functions/.../fetch",
    "populate": "https://api.wetransform.com/power-functions/.../populate",
    "abort": "https://api.wetransform.com/power-functions/.../abort"
  },
  "pages": 12
}

2. The FETCH Endpoint

Use the fetch URL provided in the trigger to retrieve the data to transform. It returns up to 1000 rows per page.

{
  "success": true,
  "payload": {
    "rows": [
      {
        "row": "1",
        "arguments": [
          { "name": "EAN", "value": "1234567890123" }
        ]
      }
    ]
  }
}

3. The POPULATE Endpoint

Once your app has processed the data, send the results back using the populate URL.

{
  "outcomes": [
    {
      "row": "1",
      "outcome": "Transform Result"
    }
  ]
}

Security & Verification

In Callback mode, to ensure the requests come from WeTransform, you must verify the X-Signature header using HMAC SHA256. In Fetch mode, this does not apply: authenticate WeTransform on your side with the {token} placeholder instead.

function verify_signature($body, $signature, $secret) {
    $expected = hash_hmac('sha256', $body, $secret);
    return hash_equals($expected, $signature);
}

const crypto = require('crypto');
function verifySignature(body, signature, secret) {
    const expected = crypto.createHmac('sha256', secret).update(body).digest('hex');
    return expected === signature;
}