Ollama's gemma4 renderer silently drops tool parameters named type or description, and the model invents a value
TL;DR : define a tool for a gemma4 model in Ollama with a parameter whose name is type , description , properties , required or nullable , and the model is never shown that parameter's definition. It is still listed under required:[…] in the rendered declaration, so the model knows it must supply something and has no idea what. On gemma4:e2b at temperature 0 the result is an invented value —…
When defining a tool in Ollama for a Gemma4 model, it's common to include parameters named type, description, properties, required, and nullable. However, the model does not receive the definition of these parameters. Despite this, it still shows that the parameter is required in the rendered declaration, so the model knows it must supply something but has no idea what it should be.
On Gemma4:e2b with a temperature of 0, the model invents a value for a parameter whose legal values are only urgent_A7 and routine_B3. On the reporter's Gemma4:26b model, the argument is omitted entirely. This occurs because the Go port of the reference Jinja template dropped one argument—the format_parameters macro takes filter_keys=false and filters schema keywords in one call site, but the Go writeSchemaProperties function serves all four arguments. By restoring the argument, the issue is resolved.
Written by urgent.news from Dev.to's reporting — not their text. Machine-written — may contain errors; check the original before relying on it.
