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Antigravity Codex MCP

Antigravity Codex MCP

by ustc-fyk
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Start a project AGY session

antigravity_start_session
Read-only

Start an Antigravity session for an enabled project, saving it as active and returning its conversation ID. Consumes one model turn to enable AI-powered code review and delegation within a controlled context.

Instructions

Create a new AGY conversation for an enabled project, save it as active, and return its conversation ID. Consumes one Antigravity model turn.

Tool call template

Replace each placeholder with a value matching the input schema. Only required parameters are included; add optional parameters as needed.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {
      "project_root": "<project_root>"
    },
    "name": "antigravity_start_session"
  }
}

Input Schema

NameRequiredDescriptionDefault
modelNoOptional Antigravity model slug; omit to use the account default.
effortNo
promptNoRegister this project conversation and reply exactly: AGY_PROJECT_READY
project_rootYesAbsolute root directory of the current Codex project.
timeout_secondsNo
max_response_charsNo

Schema Changelog

Changes observed during successful MCP inspections.

  1. First observedv0.3.0

TDQS

B3.1/5.0
Behavior1/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

The description says the tool creates, saves, and consumes a turn, but the annotations declare readOnlyHint=true. This is a direct contradiction because creating a session and marking it active are state-affecting operations. The description also usefully discloses turn consumption, but the contradiction with the annotations invalidates the transparency score.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness5/5

Is the description appropriately sized, front-loaded, and free of redundancy?

The description is brief, front-loaded, and each clause earns its place. It states the action, the state change, the return value, and the cost.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness2/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

The tool has six parameters, no output schema, and only one required field. The description does not explain preconditions like what happens for disabled projects, the meaning of the default prompt, error behavior, or timeout/response limitations, so this is not fully contextual for an agent selecting and invoking the tool.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters2/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is only 33%, with effort, timeout_seconds, max_response_chars, and prompt lacking parsing in the schema. The description adds no parameter-level guidance or clarification, so the agent gets little help for several self-explanatory but still underspecified options.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

The description states a specific action: create a new AGY conversation, save it as active, and return its conversation ID. It clearly distinguishes itself from sibling tools like antigravity_get_active_session and antigravity_list_sessions by focusing on creating a new session rather than reading or listing existing ones.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines3/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

The description implies this tool is used when creating a new AGY session for an enabled project, and mentions that one model turn is consumed. However, it provides no explicit guidance about when not to use it or when to prefer a sibling tool such as antigravity_continue or antigravity_ask.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

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