What it does
The Call Agent tool allows your agents to communicate with and delegate tasks to other agents on the Aster platform. Perfect for creating agent workflows, specialized task delegation, and building complex multi-agent systems.
Key features
- Call any agent on your Aster platform
- Continue conversations across multiple interactions
- Maintain conversation threads for context
- Access to called agent’s capabilities and knowledge
- Seamless agent-to-agent communication
Parameters
Common use cases
Specialized task delegation
Delegate data analysis to a specialized analytics agent.
Multi-step workflows
Continue a conversation thread for complex workflows.
Expert consultation
Get expert review from specialized agents.
Content creation pipeline
Start a content creation workflow with writing specialists.
Quality assurance
Add quality control steps to your workflows.
Customer support escalation
Escalate complex issues to specialized support agents.
Agent collaboration patterns
Sequential workflow
- Agent A calls Agent B for initial analysis
- Agent B returns results to Agent A
- Agent A calls Agent C for final processing
- Agent C delivers final output
Parallel processing
- Call multiple specialized agents simultaneously
- Combine their outputs for comprehensive results
- Useful for multi-perspective analysis
Iterative refinement
- Use
respondToThreadId to continue conversations
- Refine outputs through multiple interactions
- Build complex solutions step by step
Configuring callable agents
When you enable call_agent on an agent, you choose which agents it’s allowed to call:
Allow all agents in organization (default) — The agent can call any non-deleted agent in the org. This is ideal when paired with Manage Agents, which lets the agent dynamically discover available agents at runtime.
Select specific agents — Restrict the agent to a curated allowlist. Use the agent selector modal to pick exactly which agents are callable. This is better when you want tight control over which agents can be reached.
Both modes are configured in Control Hub → Edit Agent → Call Agent tool section.
Finding agents to call
Agents are called by name (not ID). The agent can discover names by:
- Using Manage Agents with
action: "list" to see all agents in the org
- Having agent names included in its system prompt
- Being told by the user which agent to call
What you get back
The sub-agent runs asynchronously; the call returns a summary of its work:
When pointing a user at the run, share conversationUrl as a markdown link — the raw thread
id isn’t clickable and sends people hunting through Control Hub history.
Best practices
- Use clear, specific messages when calling agents
- Include relevant context and background information
- Use thread IDs to maintain conversation continuity
- Choose the right agent for each specific task
- Monitor agent interactions for workflow optimization
- Set up proper agent permissions and access controls
Troubleshooting
“Agent not found”
- The agent name must match exactly (case-insensitive). Check spelling
- If using a specific allowlist, verify the target agent is in the list
- The target agent may have been deleted
“No callable agents configured”
- The agent has
call_agent enabled but is set to “Select specific agents” with none selected
- Either toggle “Allow all agents” on, or select specific agents in the modal
- Manage Agents - Discover available agents before calling them
- Send Email - Notify stakeholders of agent interactions
- Run Code - Process agent responses programmatically
