Disclaimer: These documents reflect our current understanding of each agent’s hook system
and extensibility surface. They are maintained as working references for symposium development,
not as a substitute for each project’s official documentation. Details may be outdated or
incomplete — always consult the primary sources linked in each agent’s page.
For each agent it supports, symposium needs to know:
Hook registration — where and how to write config so the agent calls cargo-agents hookHook I/O protocol — event names, input/output field names, exit code semanticsExtension installation — where skill files go (project and global)Custom instructions — where the agent reads project-level instructions
The tables below summarize the answers for each agent. Individual agent pages contain the full reference. A ? indicates information we have not yet documented.
Agent Project config path Global config path Format
Claude Code .claude/settings.json~/.claude/settings.jsonJSON, hooks key with matcher groups GitHub Copilot .github/hooks/*.json~/.copilot/config.jsonJSON, version: 1 with hooks key Gemini CLI .gemini/settings.json~/.gemini/settings.jsonJSON, hooks key with matcher groups Codex CLI .codex/hooks.json~/.codex/hooks.jsonJSON, hooks key with matcher groups Kiro .kiro/agents/*.json~/.kiro/agents/*.jsonJSON, hooks key in agent config OpenCode .opencode/plugins/~/.config/opencode/plugins/JS/TS plugins (not shell hooks) Goose (no hooks) (no hooks) N/A
Agent Command field Platform-specific?
Claude Code commandNo GitHub Copilot bash / powershellYes Gemini CLI commandNo Codex CLI commandNo Kiro commandNo OpenCode N/A (JS function) N/A Goose N/A N/A
Agent Default timeout Unit
Claude Code 600 seconds GitHub Copilot 30 seconds (timeoutSec) Gemini CLI 60,000 milliseconds (timeout) Codex CLI 600 seconds (timeout or timeoutSec) Kiro 30,000 milliseconds (timeout_ms) OpenCode 60,000 milliseconds (community hooks plugin) Goose N/A N/A
Symposium registers hooks for four events. Each agent uses different names and casing conventions.
Symposium event Claude Code Copilot Gemini CLI Codex CLI Kiro CLI OpenCode Goose
pre-tool-use PreToolUsepreToolUseBeforeToolPreToolUsepreToolUsetool.execute.beforeN/A post-tool-use PostToolUsepostToolUseAfterToolPostToolUsepostToolUsetool.execute.afterN/A user-prompt-submit UserPromptSubmituserPromptSubmittedBeforeAgentUserPromptSubmituserPromptSubmitmessage.updated (filter by role)N/A session-start SessionStartsessionStartSessionStartSessionStartagentSpawnsession.createdN/A
Not all events can block the action in all agents.
Agent Pre-tool-use can block? Post-tool-use can block? User-prompt can block? Session-start can block?
Claude Code Yes No Yes (exit 2) No GitHub Copilot Yes No No No Gemini CLI Yes Yes (block result) Yes (deny discards message) No Codex CLI Yes Yes (continue: false) Yes (continue: false) Yes (continue: false) Kiro Yes (exit 2) No No No OpenCode Yes (throw Error) No No (observe only) No (observe only) Goose N/A N/A N/A N/A
Agent Tool name field Tool args field Session/context fields
Claude Code tool_nametool_input (object)session_id, cwd, hook_event_nameGitHub Copilot toolNametoolArgs (JSON string )timestamp, cwdGemini CLI tool_nametool_input (object)session_id, cwd, hook_event_name, timestampCodex CLI tool_nametool_input (object)session_id, cwd, hook_event_name, modelKiro tool_nametool_input (object)hook_event_name, cwdOpenCode toolargs (mutable output object)sessionID, callIDGoose N/A N/A N/A
Agent Permission decision field Decision values Modified input field Nesting
Claude Code permissionDecisionallow, deny, ask, defer updatedInputnested in hookSpecificOutput GitHub Copilot permissionDecisionallow, deny, ask modifiedArgsflat Gemini CLI decisionallow, deny tool_inputnested in hookSpecificOutput Codex CLI decision or permissionDecisionblock/deny (not yet implemented) flat or nested hookSpecificOutput Kiro (exit code only) exit 0 = allow, exit 2 = block (not supported) N/A OpenCode (throw to block) allow (return) / deny (throw) mutate output.args JS mutation Goose N/A N/A N/A N/A
All shell-based agents use the same convention (where applicable):
Code Meaning
0Success; stdout parsed as JSON 2Block/deny; stderr used as reason Other Non-blocking warning, action proceeds
Exceptions : Copilot uses exit 0 = allow, non-zero = deny (no special meaning for exit 2). OpenCode uses JS exceptions, not exit codes.
Agent Project skills path Global skills path
Claude Code .claude/skills/<name>/SKILL.md~/.claude/skills/<name>/SKILL.mdGitHub Copilot .agents/skills/<name>/SKILL.md(none) Gemini CLI .agents/skills/<name>/SKILL.md~/.gemini/skills/<name>/SKILL.mdCodex CLI .agents/skills/<name>/SKILL.md~/.agents/skills/<name>/SKILL.mdKiro .kiro/skills/<name>/SKILL.md~/.kiro/skills/<name>/SKILL.mdOpenCode .agents/skills/<name>/SKILL.md~/.agents/skills/<name>/SKILL.mdGoose (N/A — uses MCP extensions) (N/A)
Symposium uses the vendor-neutral .agents/skills/ path whenever the agent supports it, falling back to agent-specific paths (e.g., .claude/skills/, .kiro/skills/) when required. Codex CLI and OpenCode also support .agents/skills/ natively.
Agent Project instructions Global instructions
Claude Code CLAUDE.md, .claude/CLAUDE.md~/.claude/CLAUDE.mdGitHub Copilot .github/copilot-instructions.md, AGENTS.md~/.copilot/copilot-instructions.mdGemini CLI GEMINI.md (walks up to .git)~/.gemini/GEMINI.mdCodex CLI AGENTS.md (each dir level)~/.codex/AGENTS.mdKiro .kiro/steering/*.md, AGENTS.md~/.kiro/steering/*.mdOpenCode AGENTS.md, CLAUDE.md~/.config/opencode/AGENTS.mdGoose .goosehints, AGENTS.md~/.config/goose/.goosehints
Relevant if symposium exposes functionality via MCP.
Agent MCP config location Format
Claude Code .claude/settings.json (mcpServers key)JSON GitHub Copilot .vscode/mcp.json (VS Code), ~/.copilot/mcp-config.json (CLI)JSON Gemini CLI .gemini/settings.json (mcpServers key)JSON Codex CLI .codex/config.toml / ~/.codex/config.toml (mcp_servers key)TOML Kiro .kiro/settings/mcp.json, ~/.kiro/settings/mcp.jsonJSON OpenCode opencode.json (mcp key)JSON Goose ~/.config/goose/config.yaml (extensions key)YAML