Google Antigravity (antigravity)

Output

.agent/AGENTS.md               # canonical entry-point pointer body (written by sync)
.agents/rules/<name>.md        # one per rule
.agents/agents/<name>/agent.md # one per agent (custom subagent)
.agents/skills/<name>/SKILL.md # one folder per skill (Antigravity's native path)
.agents/mcp_config.json        # when MCP entries exist

Antigravity reads project instructions from a top-level AGENTS.md-style file, per-rule files under .agents/rules/, and custom subagents under .agents/agents/. The adapter emits all three; sync writes the pointer body to .agent/AGENTS.md.

The entry-point path stays under .agent/ (singular) to avoid clashing with codex / amp / warp at the project-root AGENTS.md. Rules, skills, and MCP default to the plural .agents/ form Antigravity itself now prefers (rules, skills), which still "maintains backward support" for the singular paths.

A stale managed tree at the pre-plural .agent/rules / .agent/skills defaults is swept on sync unless outputs.antigravity.rules-dir / skills-dir opts back into the legacy path explicitly.

• Agents: one custom subagent per agent at .agents/agents/<name>/agent.md, the nested workspace form documented alongside the flat form in Antigravity's subagent reference.
  • Goose and OpenHands only scan top-level .md files in the same root, so the nested form keeps Antigravity's restricted model tier separate from their free-form model IDs (#717). Frontmatter carries name and description, both required; the body defines the system prompt.
  • A managed flat profile from an earlier sync is removed by the sync ledger when no enabled target still writes it. When Goose or OpenHands is enabled, that flat path remains as their current shared output. import antigravity prefers nested profiles and falls back to legacy flat files only when no nested profile exists, so it does not ingest co-located Goose or OpenHands agents.
  • Agents previously flattened into .agents/rules/agent-<name>.md, a path the subagent loader never reads (#638); a managed copy at the old name is swept for every current agent.
  • A generic tools list never reaches this file: Antigravity's vocabulary is its own (view_file, replace_file_content, grep_search, run_command, ...) with no name in common with agnostic-ai's Claude-style set, and the vendor warns that "Specifying an unmapped or misspelled tool name in the tools list may cause the subagent process to hang during execution". It drops with a coverage note; set x-antigravity.tools to write Antigravity's own names.
  • model is a three-value tier enum (inherit, flash, pro), not a model ID, so a value outside it drops the same way.
  • Every other documented key (mainAgent, subagent, commandExecutionPolicy, mcpServers, skills/plugins) reaches the file through x-antigravity too.
• Skills: one folder per skill under .agents/skills/<name>/SKILL.md, Antigravity's native skills layout. It's the same tree Codex, Amp, Zed, Crush, and OpenHands share, so identical skill folders dedupe. The SKILL.md frontmatter is reduced to name + description; the body follows. Sibling files next to the source SKILL.md (helper scripts, fixtures) are copied byte-for-byte into the emitted folder.
• MCP: servers land in .agents/mcp_config.json under a single mcpServers object (antigravity.google/docs/ide/mcp).
  • Remote servers carry serverUrl. The vendor doc states the legacy url / httpUrl field names "are not supported," so this is a dedicated schema, not the shared mcpServers-with-url shape claude and cursor use.
  • stdio servers carry command, args, env, and cwd; remote servers add headers.
  • Both transports accept disabled under that literal name (see disabled support by target), unlike codex and kilo which map it onto their own enabled: false.
  • Three more documented fields (authProviderType, oauth, disabledTools, same page) have no dedicated mapping. They, description, roots, and any field the vendor adds next reach the file through x-antigravity instead, the same escape hatch Zed and Warp give their own unmapped fields.
  • import antigravity reads .agents/mcp_config.json back, renaming serverUrl to the spec's generic url and preserving any other field under x-antigravity the same way.
• Hooks: merge into .agents/hooks.json (override via outputs.antigravity.hooks-file): "Hooks are configured in a hooks.json file located in your customization directory (e.g., .agents/ in your workspace)" (antigravity.google/docs/ide/hooks, #629).
  • The file is keyed by hook definition name, not by event, unlike every other hook target here, so each spec becomes its own top-level definition named after it and holding the one event it names.
  • That is also where enabled lives: a spec's disabled: true writes enabled: false on its own definition ("Set to false to disable the hook without removing it"), a sibling of the event key rather than a member of the handler array. This is the inverse spelling of the literal disabled this same adapter writes for MCP servers.
  • Five events exist: PreToolUse, PostToolUse, PreInvocation, PostInvocation, Stop. The first two hold {matcher, hooks: [...]} groups; for the other three "the structure is simpler (a list of handlers directly under the event key) and the matcher is ignored". This adapter writes each shape where the vendor documents it and notes a matcher set on the three that ignore it.
  • Per handler: type (optional, defaulting to "command", written explicitly here), command, and optional timeout (seconds, vendor default 30). An event outside the documented five is skipped with a coverage note rather than written as a key no handler backs.
  • Antigravity names its own tools (view_file, replace_file_content, grep_search, run_command, ...) with none in common with Claude's, so a matcher carried over from a Claude spec parses as a valid regex and then matches nothing. That case emits verbatim with a coverage note rather than a guessed rename, the same line OpenHands, Crush, and Windsurf hold.
  • The hook payload's transcriptPath resolves under ~/.gemini/antigravity-ide, the IDE's own app-data directory, confirming the IDE itself runs them (target-audit 2026-08-27, #563).

Commands remain fully unconfirmed in the public-preview docs and skip with a warning. Add on-unsupported: silent to suppress it, or wait for a future release once they stabilise.

Config keys

Import

agnostic-ai import antigravity prefers .agents/rules and .agents/skills/. It falls back to the singular .agent/rules and .agent/skills/ only when the preferred directory is absent. Skill imports include all bundled assets.

Agents and MCP servers import as described under Agents and MCP: nested profiles win over legacy flat files, and serverUrl becomes url.

Verify

1. Install Antigravity from the Google Antigravity public-preview download page.
2. Check the tree: ls .agent/AGENTS.md .agents/rules/ .agents/agents/ .agents/skills/, grep "Generated by agnostic-ai" .agents/rules/*.md for the provenance header (it sits after the frontmatter), test -f .agents/skills/*/SKILL.md, and python -m json.tool .agents/mcp_config.json > /dev/null when MCP specs exist.
3. Open the project; it surfaces .agent/AGENTS.md in the project-instructions panel with no "unrecognized file" warnings.
4. Open one of .agents/rules/<name>.md and verify the per-rule file is picked up; confirm each .agents/skills/<name>/SKILL.md loads as a skill, and any .agents/mcp_config.json server appears in the MCP panel.
5. Ask the agent to delegate to a custom subagent by name; each .agents/agents/<name>/agent.md profile is selectable in the subagent panel and its task runs to Idle rather than hanging (a hang points at an unmapped tools name, so check x-antigravity.tools against the vendor's vocabulary).
6. Trigger an agent action (e.g. ask for a refactor); the rules apply, with no schema-validation log entries referencing .agents/.