# Gemini 3 API: Built-in Tools + Custom Functions in One Call

Times of AI Desk · 2026-03-18 · Infrastructure

[https://timesof.ai/2026/03/google-gemini-3-adds-built-in-tools-and-maps-grounding](https://timesof.ai/2026/03/google-gemini-3-adds-built-in-tools-and-maps-grounding)

> Gemini API changelog (March 18): combine built-in tools (Search, Maps, etc.) with custom function calling in a single generateContent request; Grounding with Google Maps supported for Gemini 3. Less glue for multi-tool agents — still Google’s stack and Maps as the geo ground truth.

Agent builders used to orchestrate Google’s built-ins and their own functions in separate passes. The proprietary unlock: **one generateContent call** with both — plus **Maps grounding** so geo answers cite Google Maps instead of inventing streets.

**Gemini API** release notes (March 18) shipped **Built-in Tools and Function Calling Combination**: specify built-in tools (e.g. Google Search, Maps, file search, code execution) alongside custom functions in a single request. Notes also cite improved context circulation across multi-step built-in tool use. **Grounding with Google Maps** now supported for **Gemini 3** models — location, directions, places, geospatial responses grounded against Maps data with citations. Supported models listed in Gemini API references.

## Claims vs checks

Feature availability is **Google developer docs primary** (changelog). Grounding quality is vendor-claimed reduction in fabricated location detail — not an independent geo-hallucination audit here. Developer Threads/discussions corroborate March 18 timing.

## Limits

- Combination still lives inside Gemini API quotas and tool policies.
- Maps grounding is Google-centric ground truth by design.
- Multi-tool reliability depends on model version and prompt structure.

## Sources

- [Gemini API Release notes, March 18, 2026](https://ai.google.dev/gemini-api/docs/changelog) — built-in tools + function calling combination; Maps grounding for Gemini 3.
- Developer discussions noting the March 18 rollout.