Building managed agents

Managed agents on the Gemini API let you extend the Antigravity agent with your own instructions, skills, and data. You can customize the agent inline at interaction time, or save the configuration as a managed agent you invoke by ID.

Customize the Antigravity agent

The fastest way to build a custom agent is to pass your configuration inline while creating a new interaction with no registration step required. You can extend the agent in several key ways:

  • Model selection: Choose the underlying Gemini model via agent_config (defaults to Gemini 3.7 Flash).
  • System instructions: Pass inline text via system_instruction to shape behavior.
  • Tools: Override default tools (Code Execution, Search, URL Context), register remote MCP servers, or define custom functions (Function Calling).
  • Files and skills: Mount files like AGENTS.md and SKILL.md into the environment.

Here is an example of passing all three inline:

Python

from google import genai

client = genai.Client()

interaction = client.interactions.create(
    agent="antigravity-preview-05-2026",
    input="Analyze the Q1 revenue data and create a slide deck.",
    system_instruction="You are a data analyst. Always include visualizations and export results as PDF.",        
    environment={
        "type": "remote",
        "sources": [
            {
                "type": "inline",
                "target": ".agents/AGENTS.md",
                "content": "Always use matplotlib for charts. Include a summary table in every report.",
            },
            {
                "type": "inline",
                "target": ".agents/skills/slide-maker/SKILL.md",
                "content": "---\nname: slide-maker\n---\n# Slide Maker\nCreate HTML slide decks from data analysis results.",
            },
        ],
    },
)

print(interaction.output_text)

JavaScript

import { GoogleGenAI } from "@google/genai";

const client = new GoogleGenAI({});

const interaction = await client.interactions.create({
    agent: "antigravity-preview-05-2026",
    input: "Analyze the Q1 revenue data and create a slide deck.",
    system_instruction: "You are a data analyst. Always include visualizations and export results as PDF.",        
    environment: {
        type: "remote",
        sources: [
            {
                type: "inline",
                target: ".agents/AGENTS.md",
                content: "Always use matplotlib for charts. Include a summary table in every report.",
            },
            {
                type: "inline",
                target: ".agents/skills/slide-maker/SKILL.md",
                content: "---\nname: slide-maker\n---\n# Slide Maker\nCreate HTML slide decks from data analysis results.",
            },
        ],
    },
}, { timeout: 300000 });

console.log(interaction.output_text);

REST

curl -X POST "https://generativelanguage.googleapis.com/v1beta/interactions" \
-H "Content-Type: application/json" \
-H "x-goog-api-key: $GEMINI_API_KEY" \
-d '{
    "agent": "antigravity-preview-05-2026",
    "input": "Analyze the Q1 revenue data and create a slide deck.",
    "system_instruction": "You are a data analyst. Always include visualizations and export results as PDF.",
    "environment": {
        "type": "remote",
        "sources": [
            {
                "type": "inline",
                "target": ".agents/AGENTS.md",
                "content": "Always use matplotlib for charts. Include a summary table in every report."
            },
            {
                "type": "inline",
                "target": ".agents/skills/slide-maker/SKILL.md",
                "content": "---\nname: slide-maker\n---\n# Slide Maker\nCreate HTML slide decks from data analysis results."
            }
        ]
    }
}'

Everything is defined at interaction time. No need to register anything first. The Antigravity agent harness provides the runtime (code execution, file management, web access) and your configuration layers on top.

Tools and system instructions

You can customize the agent's behavior and capabilities for a specific interaction using the system_instruction and tools parameters.

  • System instructions: Use the system_instruction parameter to pass inline text that shapes the agent's behavior. This is ideal for quick tweaks you want to change per call. The system_instruction and AGENTS.md are additive; both apply when present.
  • Tools: By default, the Antigravity agent has access to code_execution, google_search, and url_context. You can override this list by passing the tools parameter at interaction time. You can also register remote MCP servers or define custom functions (function calling) to connect the agent to your own APIs and databases. For full details on available tools, see Antigravity Agent: Supported tools.

File-based customization

Agent directory structure

While you can pass configuration inline, we recommend organizing your agent's files in a structured directory. This makes it easier to manage, version control, and mount into the agent's environment.

A typical agent project directory looks like this:

my-agent/
├── AGENTS.md        # Instructions on how the agent should operate
├── skills/          # Custom skills (subfolders and SKILL.md files)
│   └── slide-maker/
│       └── SKILL.md
└── workspace/       # Initial data files and knowledge

The Antigravity runtime scans .agents/ (and the root of the environment) for these files.

AGENTS.md

The agent automatically loads .agents/AGENTS.md (or /.agents/AGENTS.md) from the environment as system instructions on startup. Use AGENTS.md for long-form persona definitions, detailed guidelines, and instructions you want to version control alongside your code.

Mount an AGENTS.md using an inline source:

Python

from google import genai

client = genai.Client()

interaction = client.interactions.create(
    agent="antigravity-preview-05-2026",
    input="Analyze the Q1 revenue data and create a report.",
    system_instruction="You are a data analyst. Always include visualizations and export results as PDF.",
    environment={
        "type": "remote",
        "sources": [
            {
                "type": "inline",
                "target": ".agents/AGENTS.md",
                "content": "Always use matplotlib for charts. Include a summary table in every report.",
            },
        ],
    },
)

print(interaction.output_text)

JavaScript

import { GoogleGenAI } from "@google/genai";

const client = new GoogleGenAI({});

const interaction = await client.interactions.create({
    agent: "antigravity-preview-05-2026",
    input: "Analyze the Q1 revenue data and create a report.",
    system_instruction: "You are a data analyst. Always include visualizations and export results as PDF.",
    environment: {
        type: "remote",
        sources: [
            {
                type: "inline",
                target: ".agents/AGENTS.md",
                content: "Always use matplotlib for charts. Include a summary table in every report.",
            },
        ],
    },
}, { timeout: 300000 });

console.log(interaction.output_text);

REST

curl -X POST "https://generativelanguage.googleapis.com/v1beta/interactions" \
  -H "Content-Type: application/json" \
  -H "x-goog-api-key: $GEMINI_API_KEY" \
  -d '{
      "agent": "antigravity-preview-05-2026",
      "input": "Analyze the Q1 revenue data and create a report.",
      "system_instruction": "You are a data analyst. Always include visualizations and export results as PDF.",
      "environment": {
          "type": "remote",
          "sources": [
              {
                  "type": "inline",
                  "target": ".agents/AGENTS.md",
                  "content": "Always use matplotlib for charts. Include a summary table in every report."
              }
          ]
      }
  }'

Skills: SKILL.md

Skills are files that extend the agent's capabilities. Place them under .agents/skills/<skill-name>/SKILL.md and the harness auto-discovers and registers them.

.agents/
├── AGENTS.md
└── skills/
    └── slide-maker/
        └── SKILL.md

Mount a skill using an inline source:

Python

from google import genai

client = genai.Client()

interaction = client.interactions.create(
    agent="antigravity-preview-05-2026",
    input="Create a presentation about our Q1 results.",
    system_instruction="You create presentations from data.",
    environment={
        "type": "remote",
        "sources": [
            {
                "type": "inline",
                "target": ".agents/skills/slide-maker/SKILL.md",
                "content": "---\nname: slide-maker\ndescription: Create HTML slide decks\n---\n# Slide Maker\n\nWhen asked to create a presentation:\n1. Analyze the input data\n2. Create an HTML slide deck with reveal.js\n3. Save to /workspace/output/slides.html",
            },
        ],
    },
)

print(interaction.output_text)

JavaScript

import { GoogleGenAI } from "@google/genai";

const client = new GoogleGenAI({});

const interaction = await client.interactions.create({
    agent: "antigravity-preview-05-2026",
    input: "Create a presentation about our Q1 results.",
    system_instruction: "You create presentations from data.",
    environment: {
        type: "remote",
        sources: [
            {
                type: "inline",
                target: ".agents/skills/slide-maker/SKILL.md",
                content: "---\nname: slide-maker\ndescription: Create HTML slide decks\n---\n# Slide Maker\n\nWhen asked to create a presentation:\n1. Analyze the input data\n2. Create an HTML slide deck with reveal.js\n3. Save to /workspace/output/slides.html",
            },
        ],
    },
}, { timeout: 300000 });

console.log(interaction.output_text);

REST

curl -X POST "https://generativelanguage.googleapis.com/v1beta/interactions" \
  -H "Content-Type: application/json" \
  -H "x-goog-api-key: $GEMINI_API_KEY" \
  -d '{
      "agent": "antigravity-preview-05-2026",
      "input": "Create a presentation about our Q1 results.",
      "system_instruction": "You create presentations from data.",
      "environment": {
          "type": "remote",
          "sources": [
              {
                  "type": "inline",
                  "target": ".agents/skills/slide-maker/SKILL.md",
                  "content": "---\nname: slide-maker\ndescription: Create HTML slide decks\n---\n# Slide Maker\n\nWhen asked to create a presentation:\n1. Analyze the input data\n2. Create an HTML slide deck with reveal.js\n3. Save to /workspace/output/slides.html"
              }
          ]
      }
  }'

Skills loaded from .agents/skills/ and /.agents/skills/ are both discovered automatically.

Create a managed agent

Once you've iterated on your configuration, you can create it as a managed agent with agents.create. This lets you invoke the agent by ID without repeating the configuration each time.

The id you specify when creating a managed agent must be unique to your project and must not start with reserved prefixes (e.g., google-, gemini-). See Agent ID restrictions for the full list of restricted prefixes.

From sources

Specify base_agent, id, agent_config, system_instruction and base_environment with sources. The platform provisions a fresh sandbox with your files on every invocation. See Environments for available source types (Git, GCS, inline).

Python

from google import genai

client = genai.Client()

agent = client.agents.create(
    id="data-analyst",
    base_agent="antigravity-preview-05-2026",
    agent_config={
        "type": "antigravity",
        "model": "gemini-3.7-flash",
    },
    system_instruction="You are a data analyst. Always include visualizations and export results as PDF.",
    base_environment={
        "type": "remote",
        "sources": [
            {
                "type": "inline",
                "target": ".agents/AGENTS.md",
                "content": "Always use matplotlib for charts. Include a summary table in every report.",
            },
            {
                "type": "inline",
                "target": ".agents/skills/slide-maker/SKILL.md",
                "content": "---\nname: slide-maker\n---\n# Slide Maker\nCreate HTML slide decks from data analysis results.",
            },
            {
                "type": "repository",
                "source": "https://github.com/my-org/analysis-templates",
                "target": "/workspace/templates",
            },
        ],
    },
)

print(f"Created agent: {agent.id}")

JavaScript

import { GoogleGenAI } from "@google/genai";

const client = new GoogleGenAI({});

const agent = await client.agents.create({
    id: "data-analyst",
    base_agent: "antigravity-preview-05-2026",
    agent_config: {
        type: "antigravity",
        model: "gemini-3.7-flash",
    },
    system_instruction: "You are a data analyst. Always include visualizations and export results as PDF.",
    base_environment: {
        type: "remote",
        sources: [
            {
                type: "inline",
                target: ".agents/AGENTS.md",
                content: "Always use matplotlib for charts. Include a summary table in every report.",
            },
            {
                type: "inline",
                target: ".agents/skills/slide-maker/SKILL.md",
                content: "---\nname: slide-maker\n---\n# Slide Maker\nCreate HTML slide decks from data analysis results.",
            },
            {
                type: "repository",
                source: "https://github.com/my-org/analysis-templates",
                target: "/workspace/templates",
            },
        ],
    },
});

console.log(`Created agent: ${agent.id}`);

REST

curl -X POST "https://generativelanguage.googleapis.com/v1beta/agents" \
-H "Content-Type: application/json" \
-H "x-goog-api-key: $GEMINI_API_KEY" \
-d '{
    "id": "data-analyst",
    "base_agent": "antigravity-preview-05-2026",
    "agent_config": {
        "type": "antigravity",
        "model": "gemini-3.7-flash"
    },
    "system_instruction": "You are a data analyst. Always include visualizations and export results as PDF.",
    "base_environment": {
        "type": "remote",
        "sources": [
            {
                "type": "inline",
                "target": ".agents/AGENTS.md",
                "content": "Always use matplotlib for charts. Include a summary table in every report."
            },
            {
                "type": "inline",
                "target": ".agents/skills/slide-maker/SKILL.md",
                "content": "---\nname: slide-maker\n---\n# Slide Maker\nCreate HTML slide decks from data analysis results."
            },
            {
                "type": "repository",
                "source": "https://github.com/my-org/analysis-templates",
                "target": "/workspace/templates"
            }
        ]
    }
}'

From an existing environment (fork)

Iterate with the base Antigravity agent until the environment is right (packages installed, files in place), then fork it into a managed agent.

Python

from google import genai

client = genai.Client()

# Step 1: set up the environment interactively
interaction = client.interactions.create(
    agent="antigravity-preview-05-2026",
    input="Install pandas, matplotlib, and seaborn. Create an analysis template at /workspace/template.py.",
    environment="remote",
)

# Step 2: fork that environment into a managed agent

agent = client.agents.create(
    id="my-data-analyst",
    base_agent="antigravity-preview-05-2026",
    system_instruction="You are a data analyst. Use the template at /workspace/template.py for all reports.",
    base_environment=interaction.environment_id,
)

print(f"Forked agent successfully: {agent.id}")

JavaScript

import { GoogleGenAI } from "@google/genai";