Documentation Index
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Build a customer greeting agent, then extend it with tools that connect to external APIs. By the end, you know how to:
- Define an agent with identity, goal, and persona
- Test your agent in the Studio chat and read trace output
- Define tool contracts (inline, HTTP, MCP, and sandbox)
- Create reusable tool files and import them
- Handle tool results and errors
Prerequisites
- An Agent Platform 2.0 account with at least one project
- Access to Studio (the visual development environment)
- Familiarity with YAML-like syntax (helpful but not required)
What You’ll Build
You start by creating a simple agent — a coffee shop greeter that answers customer questions using nothing but an LLM. Then you build a travel assistant agent with tools that fetch real data from external APIs. Together, these two exercises cover the full foundation of agent development in ABL.
Create Your First Agent
Step 1: Create a new project
Open Studio and select New Project from the dashboard. Name it bean-and-brew and select Blank Project as the template.
Studio creates the project and opens the editor.
Step 2: Define the agent
Create a new agent file named greeter.agent.abl. Paste the following ABL definition:
AGENT: Customer_Greeter
EXECUTION:
model: claude-sonnet-4-5-20250929
GOAL: |
Welcome visitors to Bean & Brew coffee shop. Answer questions about
the menu, store hours, and location. Keep responses friendly, concise,
and on-topic. If the customer asks something outside your knowledge,
politely let them know and suggest they contact the store directly.
PERSONA: |
Warm, friendly barista who loves coffee. Uses casual but professional
language. Keeps answers short and helpful. Occasionally mentions
seasonal specials to keep the conversation engaging.
LIMITATIONS:
- Cannot process orders or payments
- Cannot access real-time inventory
- Cannot make reservations
INSTRUCTIONS: |
1. Greet the customer warmly when they first message
2. Answer questions about the menu, hours, or location
3. If asked about placing an order, explain that online ordering
is coming soon and suggest visiting the store
4. Keep responses under 3 sentences when possible
FLOW block to give an agent structured steps (covered in the next tutorial), but without one the agent handles conversations entirely through LLM reasoning.
Step 3: Understand the key blocks
Here is what each block does:
AGENT — The unique name for your agent. Use underscores instead of spaces.
EXECUTION — Specifies which LLM model powers the agent.
GOAL — The agent’s primary objective. The LLM uses this as its core instruction. Use the pipe (|) character for multi-line text.
PERSONA — Defines the agent’s personality and communication style. This shapes the tone of every response.
LIMITATIONS — Explicit boundaries the agent must not cross. The LLM respects these constraints during reasoning.
INSTRUCTIONS — Step-by-step guidance for how the agent should handle conversations.
Step 4: Test in Studio chat
Open the Chat panel in Studio. Type a message:
The agent responds with a greeting matching the persona you defined — warm, friendly, coffee-themed.
Try a few more messages:
What are your store hours?
Do you have oat milk lattes?
Can I place an order for pickup?
Step 5: Review the trace output
Open the Traces panel in Studio. Select the most recent session to see the full execution trace.
The trace shows:
- Input — The user message received
- Reasoning — How the LLM interpreted the message against the goal and instructions
- Output — The response generated
- Latency — Time taken for each step
Each message exchange appears as a separate trace event. This is your primary debugging tool for understanding why an agent responded a certain way.
Step 6: Refine the persona
Update the PERSONA block to add more character:
PERSONA: |
Warm, friendly barista named Alex who has worked at Bean & Brew
for three years. Loves recommending the house blend and seasonal
specials. Uses casual but professional language. Occasionally
asks customers about their day. Keeps answers short and helpful.
Step 7: Add a completion condition
Add a COMPLETE block to define when the conversation is finished:
COMPLETE:
- WHEN: user.says_goodbye == true
RESPOND: "Thanks for stopping by Bean & Brew! See you next time."
COMPLETE block tells the Runtime when to end the session. Without it, the conversation continues until the user disconnects or the session times out.
Full greeter definition
Here is the complete greeter.agent.abl file:
AGENT: Customer_Greeter
EXECUTION:
model: claude-sonnet-4-5-20250929
GOAL: |
Welcome visitors to Bean & Brew coffee shop. Answer questions about
the menu, store hours, and location. Keep responses friendly, concise,
and on-topic. If the customer asks something outside your knowledge,
politely let them know and suggest they contact the store directly.
PERSONA: |
Warm, friendly barista named Alex who has worked at Bean & Brew
for three years. Loves recommending the house blend and seasonal
specials. Uses casual but professional language. Occasionally
asks customers about their day. Keeps answers short and helpful.
LIMITATIONS:
- Cannot process orders or payments
- Cannot access real-time inventory
- Cannot make reservations
INSTRUCTIONS: |
1. Greet the customer warmly when they first message
2. Answer questions about the menu, hours, or location
3. If asked about placing an order, explain that online ordering
is coming soon and suggest visiting the store
4. Keep responses under 3 sentences when possible
COMPLETE:
- WHEN: user.says_goodbye == true
RESPOND: "Thanks for stopping by Bean & Brew! See you next time."
Now that you have a working agent, give it the ability to call external APIs. You define tools three different ways: inline contracts, HTTP bindings, and MCP bindings.
Create a new agent file named travel_assistant.agent.abl with an inline tool definition:
AGENT: Travel_Assistant
EXECUTION:
model: claude-sonnet-4-5-20250929
GOAL: |
Help users find hotels and plan their trips. Search for available
hotels based on destination, dates, and number of guests. Provide
weather information for travel destinations.
PERSONA: |
Knowledgeable travel advisor who gives clear, practical recommendations.
Presents search results in an organized format with key details like
price, rating, and location.
TOOLS:
search_hotels(destination: string, checkin: date, checkout: date, guests: number) -> {hotels: array}
description: "Search for available hotels by destination and dates"
get_hotel_details(hotel_id: string) -> {name: string, rating: number, amenities: array, photos: array}
description: "Get detailed information about a specific hotel"
INSTRUCTIONS: |
1. Ask the user where and when they want to travel
2. Search for hotels using the search_hotels tool
3. Present the top results with price, rating, and location
4. Offer to show details for any specific hotel
5. If no hotels are found, suggest adjusting dates or destination
TOOLS block defines the contract for each tool: its name, parameters with types, return type, and a description. The Runtime resolves these contracts to actual implementations at deployment time.
When multiple agents share the same API, define tools in a separate .tools.abl file. Create tools/hotels-api.tools.abl:
TOOLS:
base_url: "https://api.hotels.example.com/v1"
auth: bearer
timeout: 5000
retry: 3
search_hotels(destination: string, checkin: date, checkout: date) -> Hotel[]
type: http
endpoint: "/search"
method: POST
description: "Search available hotels"
get_hotel(hotel_id: string) -> Hotel
type: http
endpoint: "/hotels/{hotel_id}"
method: GET
description: "Get hotel details by ID"
get_reviews(hotel_id: string, limit: number = 10) -> Review[]
type: http
endpoint: "/hotels/{hotel_id}/reviews"
method: GET
description: "Get reviews for a hotel"
base_url, auth, timeout, retry) apply to every tool in the file. Each tool specifies its HTTP binding: endpoint path, method, and description.
Update your agent to import tools from the shared file using FROM ... USE:
AGENT: Travel_Assistant
EXECUTION:
model: claude-sonnet-4-5-20250929
GOAL: |
Help users find hotels and plan their trips. Search for available
hotels based on destination, dates, and number of guests. Provide
weather information for travel destinations.
PERSONA: |
Knowledgeable travel advisor who gives clear, practical recommendations.
Presents search results in an organized format with key details like
price, rating, and location.
TOOLS:
FROM "./tools/hotels-api.tools.abl" USE: search_hotels, get_hotel
format_results(hotels: Hotel[]) -> string
description: "Format hotel results for display"
get_weather(location: string) -> {temp: number, conditions: string}
type: mcp
server: "weather-service"
tool: "get_current_weather"
description: "Get current weather for a destination"
INSTRUCTIONS: |
1. Ask the user where and when they want to travel
2. Search for hotels using the search_hotels tool
3. Check the weather at the destination using get_weather
4. Present the top results with price, rating, and weather info
5. Offer to show details for any specific hotel
- Imported HTTP tools (
search_hotels, get_hotel) — loaded from the shared file with full HTTP binding
- Contract-only tool (
format_results) — the Runtime injects the implementation at deployment time
- MCP tool (
get_weather) — connects to an external MCP server for weather data
ABL supports several tool execution types. Here is a reference for the most common ones:
TOOLS:
# HTTP tool -- calls a REST API
create_booking(hotel_id: string, guest_name: string) -> {booking_id: string}
type: http
endpoint: "/bookings"
method: POST
auth: bearer
timeout: 10000
description: "Create a hotel booking"
# MCP tool -- connects to an MCP server
get_weather(location: string) -> {temp: number, conditions: string}
type: mcp
server: "weather-service"
tool: "get_current_weather"
description: "Get current weather"
# Sandbox tool -- runs custom code in isolation
calculate_price(base_rate: number, nights: number, tax_rate: number) -> {total: number}
type: sandbox
runtime: "javascript"
entrypoint: "calculatePrice"
timeout: 5000
memory_mb: 128
description: "Calculate total booking price with tax"
# Contract-only tool -- implementation injected by the Runtime
send_confirmation(email: string, booking_id: string) -> {sent: boolean}
description: "Send booking confirmation email"
ON_SUCCESS and ON_FAIL:
search_and_show:
REASONING: false
CALL: search_hotels(destination, checkin_date, checkout_date, num_guests)
ON_SUCCESS:
RESPOND: |
Found {{hotels.length}} hotels in {{destination}}:
{{#each hotels}}
{{add @index 1}}. {{name}} - ${{price}}/night ({{rating}} stars)
{{/each}}
Which hotel interests you?
THEN: select_hotel
ON_FAIL:
RESPOND: "No hotels found for those dates. Would you like to try different dates?"
THEN: get_dates
ON_SUCCESS block runs when the tool call returns data. The ON_FAIL block runs when the tool call fails or returns no results. Both can include RESPOND messages and THEN transitions to other steps.
Step 13: Use CALL WITH for explicit parameters
For more control over tool parameters, use CALL ... WITH syntax:
validate_recipient_step:
REASONING: false
CALL: validate_recipient
WITH:
routing_number: recipient_routing
account_number: recipient_account
AS: recipientResult
ON_RESULT:
- IF: recipientResult.status == "valid"
SET:
recipient_bank = recipientResult.bank_name
recipient_name = recipientResult.account_holder
THEN: collect_amount
- IF: recipientResult.status == "INVALID_ROUTING"
RESPOND: "The routing number is invalid. Please check and try again."
THEN: collect_recipient
- ELSE:
RESPOND: "Could not verify the recipient. Please try again."
THEN: collect_recipient
WITH block maps session variables to tool parameters. The AS keyword binds the tool result to a named variable. ON_RESULT provides multi-way branching based on the result values.
Open the Chat panel in Studio and start a conversation:
I need a hotel in Paris for next week
- The agent receives the user message
- The LLM decides to call
search_hotels with the extracted parameters
- The Runtime executes the HTTP request
- The tool result flows back to the agent
- The agent formats and presents the results
Each tool call appears as a separate span in the trace tree. Select a tool span to see:
- Parameters sent — The actual values passed to the tool
- Response received — The raw data returned
- Latency — How long the tool call took
- Status — Whether the call succeeded or failed
Full travel assistant definition
AGENT: Travel_Assistant
EXECUTION:
model: claude-sonnet-4-5-20250929
GOAL: |
Help users find hotels and plan their trips. Search for available
hotels based on destination, dates, and number of guests. Provide
weather information for travel destinations.
PERSONA: |
Knowledgeable travel advisor who gives clear, practical recommendations.
Presents search results in an organized format with key details like
price, rating, and location.
TOOLS:
FROM "./tools/hotels-api.tools.abl" USE: search_hotels, get_hotel
format_results(hotels: Hotel[]) -> string
description: "Format hotel results for display"
get_weather(location: string) -> {temp: number, conditions: string}
type: mcp
server: "weather-service"
tool: "get_current_weather"
description: "Get current weather for a destination"
INSTRUCTIONS: |
1. Ask the user where and when they want to travel
2. Search for hotels using the search_hotels tool
3. Check the weather at the destination using get_weather
4. Present the top results with price, rating, and weather info
5. Offer to show details for any specific hotel
COMPLETE:
- WHEN: user.booking_complete == true
RESPOND: "Your trip is all set! Have a wonderful time."
- WHEN: user.says_goodbye == true
RESPOND: "Thanks for using our travel service. Safe travels!"
What You Learned
- AGENT, GOAL, PERSONA, and INSTRUCTIONS define your agent’s identity and behavior
- Agents reason by default, using the LLM for every response; adding a
FLOW block is optional for structured steps
- LIMITATIONS set explicit boundaries the agent respects
- COMPLETE defines when the session ends
- Studio’s chat panel lets you test agents interactively; trace output shows the full reasoning chain
- Inline tool contracts define a tool’s name, parameters, return type, and description
- Tool files (
.tools.abl) let you share tools across agents with shared configuration
- FROM … USE imports specific tools from a tool file
- ABL supports four tool types: http, mcp, sandbox, and contract-only
- ON_SUCCESS / ON_FAIL handle tool results; CALL … WITH … AS gives explicit parameter control
- ON_RESULT enables multi-way branching based on tool return values
- Tool calls appear as individual spans in the Studio trace view
Next Steps
Check out the Template Gallery in Studio for ready-made agent definitions across use cases — customer support, e-commerce, banking, and more.
