skills/docs/research/agent-capability-matrix.md

Agent Capability Matrix

Date: 2026-01-09 Status: Research complete Related: skills-fqu, Cross-agent epic

Overview

Comparison of AI coding agent capabilities for cross-agent skill portability and quality gate design.

Agent	Vendor	Open Source	Primary Language
Claude Code	Anthropic	No	TypeScript
Gemini CLI	Google	Yes (Apache 2.0)	TypeScript
OpenCode	OpenCode	Yes	Go + TypeScript
Codex CLI	OpenAI	Yes	Rust

Capability Matrix

Core Features

Capability	Claude Code	Gemini CLI	OpenCode	Codex CLI
Hooks/Lifecycle	✅ 9 events	✅ 8+ events	✅ 32+ events	⚠️ Limited
Subagent Spawning	✅ Task tool	⚠️ Via MCP	✅ Native	⚠️ Recent
File System Access	✅ Full	✅ Full	✅ Configurable	🔒 Sandboxed
Bash Execution	✅ Yes	✅ Yes	✅ Yes	✅ Yes
State Persistence	✅ Sessions	✅ Auto-save	✅ Multi-level	✅ Client-side
MCP Support	✅ Yes	✅ Yes	✅ Yes	✅ Yes
Web Search	✅ Built-in	✅ Grounded	✅ Via tool	✅ Built-in

Context & Models

Capability	Claude Code	Gemini CLI	OpenCode	Codex CLI
Context Window	200K tokens	1M (2M soon)	Model-dependent	128-400K
Auto Compaction	✅ Yes	✅ Yes	✅ Yes	✅ Yes
Model Support	Claude only	Gemini only	75+ providers	GPT-5.x
Custom Models	❌ No	❌ No	✅ Yes	❌ No

Security & Sandboxing

Capability	Claude Code	Gemini CLI	OpenCode	Codex CLI
OS Sandboxing	❌ No	❌ No	❌ No	✅ Yes
Permission System	✅ Approval	✅ Approval	✅ Granular	✅ Approval
Tool Restrictions	❌ No	✅ excludeTools	✅ Per-tool	✅ Sandbox modes
Path Restrictions	❌ No	❌ No	✅ external_directory	✅ Workspace only

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Detailed Breakdown

1. Hooks / Lifecycle Events

Critical for quality gates - hooks enable mechanical enforcement.

Claude Code

SessionStart, SessionEnd, PreToolUse, PostToolUse,
PreCompact, UserPromptSubmit, Stop, SubagentStop, Notification

• Executable scripts via hooks.json
• Timeout configurable per hook
• Can block operations (Stop hook for quality gates)

Gemini CLI

SessionStart, SessionEnd, PreCompress, BeforeModel, AfterModel,
BeforeToolSelection, Notification

• Similar to Claude Code architecture
• Scripts or npm plugin packages
• Disabled by default for security

OpenCode

32+ events including:
session.*, file.*, command.*, permission.*, message.*,
todo.*, lsp.*, pty.*, tui.*

• Most comprehensive event system
• JS/TS modules (not shell scripts)
• Plugin-based architecture

Codex CLI

Limited: notification hooks, approval hooks, event loop lifecycle

• Less mature hook system
• Community requesting more hooks
• Tool-call events with approval flags

Cross-Agent Implication: Only Claude Code and Gemini have Stop-equivalent hooks for blocking exit. OpenCode and Codex would need protocol-based enforcement.

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2. Subagent Spawning

Critical for orchestrator pattern - can any agent spawn others?

Claude Code

• Task tool - Native subagent spawning
• Multiple agent types (Explore, Plan, Bash, etc.)
• Returns results to parent
• Can run in background

Gemini CLI

• Limited native - Experimental YOLO mode
• Via MCP - PAL server enables cross-CLI spawning
• Can spawn Claude Code as subagent and vice versa

OpenCode

• Native support - Primary agents spawn subagents
• Session forking with parent tracking
• @agent-name mentions for manual invocation
• Configurable agent modes (primary/subagent/all)

Codex CLI

• Recent addition - Multi-conversation agent control
• Can run as MCP server for other agents
• Sandbox restrictions complicate spawning

Cross-Agent Implication: MCP is the universal bridge. Any agent can spawn any other via MCP server pattern.

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3. File System Access

Critical for skills - can agents read skill files?

Claude Code

• Full filesystem access
• No path restrictions
• User permission level

Gemini CLI

• Full filesystem access
• Known issue: ReadFile restricts to workspace directories
• Symlinked paths (like ~/.claude/skills/) may be blocked
• Workaround: use shell cat command

OpenCode

• Configurable permissions per operation
• external_directory permission for outside-project access
• Granular: ask/allow/deny per operation type

Codex CLI

• Sandboxed by default - workspace-only writes
• Network disabled by default
• --add-dir for selective access
• danger-full-access mode available

Cross-Agent Implication: Gemini's path restrictions (skills-bo8) are the main blocker. Skills need to be in workspace or use shell workarounds.

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4. CLI Tool Execution

Critical for skills using helper scripts.

Agent	Method	Safety
Claude Code	Bash tool	Approval prompts
Gemini CLI	run_shell_command (bash -c)	Approval prompts
OpenCode	Bash tool with glob patterns	Granular permissions
Codex CLI	! prefix or shell tool	Sandbox + approval

All agents can run CLI tools. Key differences:

• Codex has OS-level sandboxing
• OpenCode has most granular permission patterns
• Gemini and Claude have similar approval models

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5. State Persistence

Critical for quality gates - need to track review status.

Agent	Session Storage	Cross-Session Memory
Claude Code	Yes	CLAUDE.md
Gemini CLI	Auto-save to ~/.gemini/	GEMINI.md, save_memory tool
OpenCode	Multi-level	Config files
Codex CLI	Client-side only	~/.codex/sessions/

Cross-Agent Implication: For cross-agent state, need external store (jwz, beads, or simple files). Agent-native persistence is agent-specific.

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6. Built-in Tools

Claude Code (~10 tools)

Read, Write, Edit, Glob, Grep, Bash, Task, WebFetch, WebSearch, TodoWrite, NotebookEdit

Gemini CLI (12+ tools)

read_file, write_file, replace, glob, list_directory, run_shell_command, web_fetch, google_web_search, save_memory, write_todos, codebase_investigator, search_file_content, read_many_files

OpenCode

File ops, Bash, Web fetch, LSP integration, Git/VCS, PTY management, MCP servers, Custom plugins

Codex CLI

read_file, list_dir, glob_file_search, apply_patch, git, rg (search), shell, todo_write, web_search, image support

Parity: All have core file/shell/search. Differences in naming and extras (LSP, code execution, etc.)

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Cross-Agent Quality Gate Analysis

What Works Across All Agents

Component	Approach
State storage	External CLI tool (jwz, bd, or file-based)
Reviewer invocation	Any agent can spawn reviewer via Bash/MCP
Issue tracking	External CLI (beads, tissue)
Second opinions	orch works from any agent with Bash

What Doesn't Work Across Agents

Component	Problem
Stop hook	Claude/Gemini only - no equivalent in OpenCode/Codex
Mechanical blocking	Can't prevent exit without hooks
Native subagents	Different spawning mechanisms

Recommended Cross-Agent Pattern

┌─────────────────────────────────────────────┐
│  Orchestrator (any agent)                    │
│                                              │
│  1. Start work                               │
│  2. Spawn worker agent (via MCP/Bash)        │
│  3. Worker completes, posts to state store   │
│  4. Orchestrator spawns reviewer             │
│  5. Reviewer posts APPROVED/ISSUES           │
│  6. Orchestrator checks state, gates exit    │
└─────────────────────────────────────────────┘

The orchestrator enforces the gate, not hooks. Works with any agent.

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Recommendations

For Portable Skills

1. Use SKILL.md format - All agents can read markdown
2. Avoid agent-specific features - No hooks in skill logic
3. CLI tools for actions - All agents can run Bash
4. External state - beads/jwz for cross-agent coordination

For Quality Gates

1. Orchestrator pattern - Gate logic in orchestrator, not hooks
2. Protocol-based - Agents follow instructions, post to state store
3. Hybrid - Use hooks where available (Claude/Gemini), protocol elsewhere

For Subagent Research Sandbox (skills-ut4)

Agent	Sandbox Approach
Claude Code	No native sandbox - rely on Task agent type restrictions
Gemini CLI	excludeTools setting to disable write tools
OpenCode	Permission config: edit: "deny", bash: "deny"
Codex CLI	Native sandbox - best support for read-only research

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Open Questions

1. Can MCP server sandboxing be enforced by the server, not client?
2. Is there a standard for "read-only agent" across platforms?
3. Should we build a universal sandbox wrapper script?
4. How do we handle agents that ignore protocol instructions?

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References

• Claude Code Docs
• Gemini CLI GitHub
• OpenCode Docs
• Codex CLI Docs
• MCP Specification