AI Agent Returning Invalid Tool Calls? How to Validate LLM Actions

Sat, 08 Aug 2026 15:46:00 +0100

If your agent sometimes invents a tool name, omits a required argument, returns malformed JSON, or produces an action that looks plausible but cannot actually be executed, the problem is usually not “the agent is dumb.”

The problem is that raw language-model output has been allowed to cross directly into execution.

That boundary is too weak.

The simplest useful agent architecture is not:

prompt
  ↓
model
  ↓
execute whatever came back

It is:

Structured Outputs on Programmer.ie: Modern AI programming

AI Agent Returning Invalid Tool Calls? How to Validate LLM Actions