I changed a tool's schema four ways and watched three agent frameworks break differently — 36 runs measured
If you run agents with tools, this day always comes: "I need to change this tool's arguments — will the agent survive?" Tool schema changes are a daily event in agent development. An argument gets renamed. A type changes. An argument is removed. A new required argument appears. The ideal is to fix the prompt and all call sites at the same time. In practice, "the schema changed first, and the…
Changing a tool's schema can cause agent frameworks to break in different ways. To test this, 36 runs were conducted with varying levels of schema changes. The rename of an argument from text to content survived without issues across all three frameworks (Strands, LangGraph, and CrewAI). However, the type change from string to integer caused silent failures in Strands, crashes in LangGraph, and a total system outage in CrewAI.
Removing the text argument also led to silent failures in Strands and CrewAI, and a 400 error in CrewAI. Adding a new required argument that the model could infer from the schema resulted in survival for both Strands and CrewAI. The data shows that none of the frameworks are inherently safe when it comes to schema changes, suggesting the need for careful handling and monitoring.
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