Skip to main content

​
What is Goja (JS) Interceptor Logic?

If JMESPath is considered the “Fast Slicer” for generic structural pruning, Goja (JavaScript) Interceptors are the full programmable processors internally deployed into the HasMCP orchestration proxy. Goja is a pure Go implementation of ECMAScript 5.1(+). It allows API administrators to write explicit JavaScript functions that dynamically intercept and rewrite upstream payloads before they are returned to the final LLM Context Window.

​
Why Use JavaScript?

While JMESPath is fantastic for extracting fields (users[0].name), it is entirely declarative. It cannot:
  1. Mask or RegEx replace sensitive string formats safely (like wiping out the first 5 digits of an SSN).
  2. Compute mathematical sums natively (looping an array to return a final total_price).
  3. Conditionally mutate variables dynamically (if account.balance < 0, inject boolean "is_bankrupt": true).
  4. Perform complex un-nesting natively, such as executing Base64 decodes on internal payload rings.

​
How It Connects to Tools

Inside the visual dashboard natively, you simply define the Javascript snippet inside the Data Transformation block of your specific Provider Tool explicitly. Example formatting: 
input.status = "Interpreted by HasMCP";
return input;
The string returned by the generic JS intercept function completely replaces the raw REST API buffer exclusively. Your LLM agent instantly receives the procedurally mapped outputs without recognizing the physical complexity seamlessly.