Gemini API Structured Output Empty Array Failure with Web Search

What this error means

Gemini 3.1 Pro can't return structured output with empty arrays when using web search is a Gemini API failure pattern reported for developers trying to fix gemini 3.1 pro failing to return structured output with empty array fields when web search tool is enabled. Based on the imported evidence, treat this as a tool-specific troubleshooting page rather than a generic API error.

Why this happens

GitHub issue (2026-05-08) with reproducible Python code showing structured output failure when combining web search + empty array fields. Specific feature combination makes this a niche but high-value search target.

Common causes

• A specific combination of features — structured output with optional list fields, web search tool, and Gemini 3.1 Pro — causes the model to fail returning empty arrays in structured responses. This is a subtle but critical bug for developers using Gemini’s function calling with web search for data extraction tasks.
• GitHub issue (2026-05-08) with reproducible Python code showing structured output failure when combining web search + empty array fields. Specific feature combination makes this a niche but high-value search target.

Quick fixes

1. Confirm the exact error signature matches Gemini 3.1 Pro can't return structured output with empty arrays when using web search.
2. Check the Gemini API account, local tool state, and provider configuration involved in the failing workflow.
3. Compare the failing environment with a known working setup, then change one configuration value at a time.

Platform/tool-specific checks

• Verify the command, editor, extension, or API client that produced the error.
• Compare local settings with CI, deployment, or editor-level settings when the error appears in only one environment.
• Avoid deleting credentials, local model data, or project settings until the failing scope is clear.

Step-by-step troubleshooting

1. Capture the exact error message and the command, editor action, or request that triggered it.
2. Check whether the failure is account/auth, quota/rate, model/provider, local runtime, or deployment configuration.
3. Review the source evidence below and compare it with your environment.
4. Apply one change at a time and rerun the smallest failing action.
5. Keep the working fix documented for the team or deployment environment.

How to prevent it

• Keep provider/tool configuration documented.
• Record non-secret diagnostics such as tool version, provider name, model name, and command path.
• Add a lightweight check before CI or production workflows depend on the tool.

Sources checked

• https://github.com/googleapis/python-genai/issues/2395

Evidence note: GitHub issue (2026-05-08) with reproducible Python code showing structured output failure when combining web search + empty array fields. Specific feature combination makes this a niche but high-value search target.

Related errors

• Gemini structured output not working
• Gemini web search tool breaks function calling

FAQ

What should I check first?

Start with the exact Gemini 3.1 Pro can't return structured output with empty arrays when using web search text and the smallest action that reproduces it.

Can I ignore this error?

No. Treat it as a failed Gemini API workflow until the root cause is understood.

Is this guaranteed to have one fix?

No. The imported evidence supports the troubleshooting path above, but tool behavior can vary by account, plan, version, provider, and local configuration.

How do I know the fix worked?

Rerun the same command, editor action, or request. The fix is working when that action completes without Gemini 3.1 Pro can't return structured output with empty arrays when using web search.