gemini-code-execution-json-mode

Gemini Code Execution + JSON Mode Compatibility

CRITICAL: Model-Specific Behavior

For all new model selections, use Gemini 3.8 Flash (gemini-3.8-flash) or a later Flash model. Never select Gemini Pro. Older rows below document compatibility only.

Gemini 3 (gemini-3.8-flash)

CAN combine code_execution with JSON mode/structured outputs.

From Gemini 3 Developer Guide:

"Gemini 3 allows you to combine Structured Outputs with built-in tools, including Grounding with Google Search, URL Context, and Code Execution."

Gemini 2.x (gemini-2.0-flash, gemini-2.5-flash)

CANNOT combine code_execution with JSON mode/controlled generation.

Error returned:

INVALID_ARGUMENT: Unable to submit request because controlled generation
is not supported with Code Execution tool.

Summary Table

Model	Code Execution	JSON Mode	Both Together
gemini-3.8-flash	YES	YES	YES
gemini-2.0-flash	YES	YES	NO
gemini-2.5-flash	NO	YES	N/A

Architecture Implications

For Your Project dice rolling:

1. Gemini 3: Can use single-phase code_execution + JSON mode
2. Gemini 2.x: Must use two-phase JSON-first tool_requests flow
   • Phase 1: JSON mode call, LLM includes tool_requests array
   • Phase 2: Execute tools server-side, inject results, second JSON call

Code Pattern

# Gemini 3: Can enable code_execution with JSON mode
if model_name in GEMINI_3_MODELS:
    enable_code_execution = True  # Safe with JSON mode

# Gemini 2.x: Must disable code_execution when using JSON mode
if model_name in ["gemini-2.0-flash", "gemini-2.5-flash"]:
    enable_code_execution = False  # Would cause INVALID_ARGUMENT

Sources

• Gemini 3 Developer Guide
• Code Execution Documentation
• Structured Outputs Documentation

Last Updated

2025-12-16