Template Variable Catalog
This page lists all recommended template variables for message_template in approval configurations. For an overview of how approval works, see Human-in-the-Loop Approval.
| Variable | Description | Available On |
|---|
{{tool_name}} | Alias of the tool being invoked | local_tools, mcp_servers allowed_tools |
{{tool_args}} | Full tool arguments as JSON string | local_tools, mcp_servers allowed_tools |
{{tool_args.<key>}} | Specific argument value | local_tools, mcp_servers allowed_tools |
{{tool_args.<key>.<nested>}} | Nested argument value | local_tools, mcp_servers allowed_tools |
{{agent_alias}} | Alias of the agent executing the tool | All contexts |
{{agent_id}} | The agent's metadata.id | All contexts |
{{mcp_server_alias}} | Alias of the MCP server (for MCP tools) | mcp_servers allowed_tools |
Remote Agent Skill Variables
| Variable | Description | Available On |
|---|
{{skill_id}} | A2A skill ID being invoked | remote_agents allowed_skills |
{{skill_args}} | Full skill arguments as JSON string | remote_agents allowed_skills |
{{skill_args.<key>}} | Specific skill argument value | remote_agents allowed_skills |
{{remote_agent_alias}} | Alias of the remote agent | remote_agents |
Agent Delegation Variables
Used in message_template on local_agents[].approval and remote_agents[].approval. Since delegation approval gates whether a sub-agent is invoked (not a specific tool call), the available variables reference the parent agent's input context.
| Variable | Description | Available On |
|---|
{{parent.input.<key>}} | Field from the parent agent's input | local_agents, remote_agents |
{{agent_alias}} | Alias of the sub-agent being delegated to | local_agents, remote_agents |
{{agent_id}} | The parent agent's metadata.id | All contexts |
Rendering Rules
- Missing variables render as empty string (no error). This prevents template failures when tool arguments vary.
- Nested access is supported:
{{tool_args.order.details.amount}}.
- No logic -- templates are pure interpolation, not a scripting language.
- Encoding -- template output is plain text. HTML/Markdown formatting is the Runtime's responsibility.
- Runtimes MAY support additional variables beyond this catalog.