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JMESPath vs. Goja JS

Both engines reside inside the HasMCP Data Transformation pipeline to compress and reshape upstream API inputs before they arrive at the LLM. However, they are used for completely different scenarios.

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JMESPath (The Fast Slicer)

JMESPath is a declarative standard for querying JSON. It is exceptionally fast, structurally deterministic, and cannot fall into infinite loops or memory leaks.
  • Use Case: “Drop everything in this 5MB object except the users array, and only keep the name and email properties from that array.”
  • Capabilities: Filtering, projection, mapping, and extraction natively.
  • Limitations: It cannot perform math, manipulate strings (like RegEx masking), or run “If/Else” stateful logic based on runtime variables.

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Goja JS (The Stateful Processor)

Goja is an actual JavaScript environment deployed directly into the HasMCP execution proxy. It allows you to write explicit ES6 JavaScript functions that manipulate the payload procedurally.
  • Use Case: “Loop through the users array. If the balance is > $1000, add a new nested field is_vip: true. Also, use RegEx to definitively replace the first 5 digits of the ssn field with asterisks.”
  • Capabilities: Math, RegEx, string parsing, conditional stateful mapping, and array reduction.
  • Limitations: Marginally slower than JMESPath due to standard JavaScript execution overhead.
Summary: Use JMESPath for 90% of basic pruning. Use Goja JS when you must compute mathematical logic or execute string replacements (like encrypting PII) before giving the data to an LLM.
[!IMPORTANT] Execution Timeouts: Both GoJA and JMESPath interceptors have a strict 100ms execution timeout on HasMCP Cloud versions to prevent runaway queries and infinite loops. Enterprise on-prem versions can define custom timeout values on their own hosted infrastructure.