Transform

Data Transformation

Reshape requests and responses with TypeScript, redirect traffic to alternative resources, and apply conditional transforms with predicate-based triggers — all without changing your application code.

Start for Free Read the Docs

TypeScript Transforms

Write full TypeScript to mutate any part of a request or response — headers, body, URL, query params — before it leaves or arrives at the proxy.

Dynamic Redirects

Rewrite target URLs at runtime to redirect traffic to alternative resources, version-switch endpoints, or route based on request content.

Predicate Triggers

Transforms only fire when configurable predicates match — scope by method, path pattern, headers, body fields, JWT claims, or response conditions.

Transform

Programmable Request Transforms

Write TypeScript that runs inside the request pipeline. Modify headers, mutate the request body, change query parameters, or rewrite the target URL to redirect to an alternative resource — all before the request is forwarded upstream. The transform receives a typed request object and a proxy context, so routing and enrichment decisions can reference the deployment configuration.

Learn more in the docs

request-transform.ts

TypeScript

export async function transform(
  req: TransformProxyRequest,
  ctx: TransformProxyContext
) {
  // Redirect v1 → v2 endpoint
  req.url = req.url.replace(
    '/v1/', '/v2/'
  );
  // Inject client correlation header
  req.headers['x-client-id'] =
    ctx.clientId;
  return req;
}

INPOST /api/v1/orders

OUTPOST /api/v2/orders

Transform

Reshape Response Payloads

Transform the upstream response before it reaches your callers. Filter sensitive fields, rename keys, add computed properties, or translate between API versions using TypeScript running inside the response pipeline. The transform receives the full upstream response — status, headers, and parsed body — and returns whatever shape your callers expect.

Learn more in the docs

response-transform.ts

UPSTREAMCALLER

{

"data": [

{ "id": 1, "name": "Alice", "internal_score": 94 }

{ "id": 2, "name": "Bob", "internal_score": 71 }

"meta": { "total": 2, "page": 1 }

}

remove internal_score, meta.page

rename data → users, meta.total → total

Transform

Conditional Predicate Triggers

Transforms can be scoped to fire only when their predicates match. Scope by HTTP method, path pattern, request headers, body content, JWT claims, response status, or response headers — so the right transform fires for exactly the right request. Set transformMode to 'conditional' and combine multiple checks to target as broadly or narrowly as needed.

Learn more in the docs

Predicate Conditionsconditional

method·methods:POST, PUT

path·path.pattern:^/api/v1/.*

header·x-api-version:must_exist

token·claims.role:admin|editor

Awaiting match…

More RequestRocket Features