Why it matters
Creating a tool is only the first step. An agent will not automatically know when or how to use a tool unless you clearly describe its purpose, trigger conditions, and usage rules in the agent instructions. Well-written instructions ensure tools are used reliably, safely, and at the right moment in a conversation.
Key Concepts
Agent Instructions: The rules and guidance that define how an agent reasons, responds, and decides when to act.
Tool Reference: An explicit mention of a tool by name inside the agent instructions.
Trigger Conditions: Clear criteria that tell the agent exactly when a tool should be called.
Usage Rules: Constraints that prevent incorrect or repeated tool usage.
Step-by-Step: Get an Agent to Use a Tool
Create and configure the tool in the Tools section.
Open Agents and select the agent you want to update.
Click Edit agent.
Scroll to the Agent instructions section.
Add the tool in the Select tools field so the agent has access to it.
In the instructions text, explicitly name the tool.
Describe when the tool should be used.
Define any rules or constraints around its usage.
Save the agent configuration.
Example: Referencing Tools in Agent Instructions
Below is an excerpt showing how tools are referenced directly in agent instructions. The agent is told which tools exist, when to use them, and what conditions must be met before calling them.
Example snippet from Agent Instructions:
Tool Calling Rules
You have these tools. Call them only when the trigger conditions match.
1) Fetch payroll data
Tool: Fetch_Payroll_Data_Tool(last_four_ssn, phone_number_on_file)
Trigger:
Once you have BOTH:
last 4 digits of SSN
the phone number they believe is on file
Rules:
Do not call this tool again unless the caller corrects their SSN or phone number.
Do not discuss any specific payroll details before this verification.
2) Transfer call to assigned recruiter
Tool: Transfer_Call_to_Recruiter_Directly(identifier)
Trigger:
Any issue outside payroll or time scope
Caller explicitly asks to speak to their recruiter
Issue cannot be resolved on the payroll line
Rules:
Use the assigned recruiter email from the payroll tool response as the identifier.
If unavailable, use identifier "fallback".
Never say the recruiter’s email out loud.
This structure makes it clear:
Which tool to use
When to use it
What inputs are required
What behavior is allowed or restricted
Tips and Best Practices
Always refer to tools by their exact tool name.
Group tools under a dedicated section like “Tool Calling Rules”.
Write trigger conditions as bullet points, not paragraphs.
Add explicit rules to prevent repeated or incorrect tool calls.
Keep instructions deterministic and unambiguous.
Troubleshooting
Issue | Possible Cause | Fix |
Agent never uses the tool | Tool not mentioned in instructions | Explicitly reference the tool and triggers |
Agent uses tool too early | Triggers too vague | Add clear prerequisite conditions |
Tool called repeatedly | Missing usage rules | Add rules limiting repeat calls |
Agent hallucinates actions | Tool not selected for agent | Add the tool in the Select tools field |