Master Vapi tools with this step-by-step walkthrough titled Tools Tutorial – Step by Step – Vapi – Functions, DTMF, End Call, Transfers, API. The video by Henryk Brzozowski shows how to use nearly every tool and how to get them to work together effectively.
You’ll progress through Functions, Make Scenario, Attaching Tools, Tools Format/Response, End Call, Transfer Call, Send SMS, API Request, DTMF, Google Calendar, plus Twilio flows and an n8n response setup. Timestamps and resource notes help you reproduce the examples and leave feedback if something needs fixing.
Prerequisites
Before you begin building voice AI scenarios with Vapi, make sure you cover a few prerequisites so your setup and testing go smoothly. This section outlines account needs, credentials, supported platforms and the baseline technical knowledge you should have. If you skip these steps you may run into avoidable friction when wiring tools together or testing call flows.
Account requirements for Vapi, Twilio, Google Calendar, and n8n
You should create accounts for each service you plan to use: a Vapi account to author scenarios and host tools, a Twilio account for telephony and phone numbers, a Google account with Google Calendar API access if you need calendar operations, and an n8n account or instance if you prefer to run automation flows there. For Twilio, verify your phone number and, if you start with a trial account, be aware of restrictions like verified destination numbers and credits. For Google Calendar, create a project in the Google Cloud Console, enable the Calendar API, and create OAuth or service account credentials as required. For n8n, decide whether you’ll use a hosted instance or self-host; either way, ensure you have access and necessary permissions to add credentials and set webhooks.
Required API keys and credentials and where to store them securely
You will need API keys and secrets for Vapi, Twilio (Account SID, Auth Token), Google (OAuth client ID/secret or service account key), and potentially other APIs such as a Time API. Store these credentials securely in environment variables, a secrets manager, or a credential vault built into your deployment platform. Avoid embedding keys in source control or public places. For local development, use a .env file kept out of version control and use a tool like direnv or your runtime’s secret management. For production, prefer managed secret storage (cloud secret manager, HashiCorp Vault, or similar) and restrict access by role.
Supported platforms and browsers for the tools tutorial
Most Vapi tooling and dashboards are accessible via modern browsers; you should use the latest stable versions of Chrome, Firefox, Edge, or Safari for the best experience. Local development examples typically run on Node.js or Python runtimes on Windows, macOS, or Linux. If you follow the n8n instructions, n8n supports containerized or native installs and is compatible with those OS platforms. For tunnel testing (ngrok or alternatives), ensure you choose a client that runs on your OS and matches your security policies.
Basic knowledge expected: HTTP, JSON, webhooks, and voice call flow concepts
You should be comfortable reading and making HTTP requests, inspecting and manipulating JSON payloads, and understanding the concept of webhooks (HTTP callbacks triggered by events). Familiarity with voice call flows — prompts, DTMF tones, transfers, playbacks, and call lifecycle events — will help you design scenarios that behave correctly. If you know basic asynchronous programming patterns (promises, callbacks, or async/await) and how to parse logs, your troubleshooting will be much faster.
Environment Setup
This section walks through installing Vapi tools or accessing the dashboard, preparing local dev environments, verifying Twilio numbers, exposing local webhooks, and getting n8n ready if you plan to use it. The goal is to get you to a point where you can test real inbound and outbound call behavior.
Installing and configuring Vapi tools package or accessing the Vapi dashboard
If you have a Vapi CLI or tools package, install it per the platform instructions for your runtime (npm for Node, pip for Python, etc.). After installation, authenticate using API keys stored in environment variables or your system’s credential store. If you prefer the dashboard, log in to the Vapi web console and verify your workspace and organization settings. Configure any default tool directories or prompt vault access and confirm your account has permissions to create scenarios and add functions.
Setting up local development environment: Node, Python, or preferred runtime
Choose the runtime you are comfortable with. For Node.js, install a recent LTS version and use npm or yarn to manage packages. For Python, use a virtual environment and pip. Configure an editor with linting and debugging tools to speed up development. Install HTTP client utilities (curl, httpie) and JSON formatters to test endpoints. Add environment variable support so you can store credentials and change behavior between development and production.
Creating and verifying Twilio account and phone numbers for testing
Sign up for Twilio and verify any required contact information. If you use a trial account, add and verify the phone numbers you’ll call during tests. Purchase an inbound phone number if you need to accept inbound calls and configure its webhook to point to your Vapi scenario endpoint or to an intermediary like ngrok during development. Note the Twilio Account SID and Auth Token and store them securely for use by your Functions and API request tools.
Configuring ngrok or similar tunnel for local webhook testing
To receive incoming webhooks to your local machine, install ngrok or an alternative tunneling tool. Start a tunnel that forwards an external HTTPS endpoint to your local port. Use the generated HTTPS URL when configuring Twilio or other webhook providers so they can reach your development server. Keep the tunnel alive during tests and be aware of rate limits or session timeouts on free plans. For production, replace tunneling with a publicly routable endpoint or cloud deployment.
Preparing n8n instance if following the n8n version of tool response
If you follow the n8n version of tool responses, ensure your n8n instance is reachable from the services that will call it and that you have credentials configured for Twilio and Google Calendar in n8n. Create workflows that mimic the Vapi tool responses — for example, returning JSON with the expected schema — and expose webhook nodes to accept input. Test your workflows independently before integrating them into Vapi scenarios.
Vapi Overview
Here you’ll get acquainted with what Vapi offers, its core concepts, how it fits into call flows, and where resources live to help you build scenarios faster.
What Vapi provides: voice AI tools, tool orchestration, and prompt vault
Vapi provides a toolkit for building voice interactions: voice AI processing, a library of tools (Functions, DTMF handlers, transfers, SMS, API request tools), and orchestration that sequences those tools into scenarios. It also offers a Prompt Vault or Tool & Prompt Vault where you store reusable prompts and helper templates so you can reuse language and behavior across scenarios. The platform focuses on making it straightforward to orchestrate tools and external services in a call context.
Core concepts: tools, functions, scenarios, and tool responses
Tools are discrete capabilities—play audio, collect DTMF, transfer calls, or call external APIs. Functions are custom code pieces that prepare data, call third-party APIs, or perform logic. Scenarios are sequences of tools that define end-to-end call logic. Tool responses are the structured JSON outputs that signal the platform what to do next (play audio, collect input, call another tool). Understanding how these pieces interact is crucial to building predictable call flows.
How Vapi fits into a call flow and integrates with external services
Vapi sits at the orchestration layer: it decides which tool runs next, interprets tool outputs, and sends actions to the telephony provider (like Twilio). When a caller dials in, Vapi triggers a scenario, uses Functions to enrich or look up data, and issues actions such as playing prompts, collecting DTMF, transferring calls, or sending SMS through Twilio. External services are called via API request tools or Functions, and their results feed into the scenario context to influence branching logic.
Where to find documentation, Tool & Prompt Vault, and example resources
Within your Vapi workspace or dashboard you’ll find documentation, a Tool & Prompt Vault with reusable assets, and example scenarios that illustrate common patterns. Use these resources to speed up development and borrow best practices. If you have an internal knowledge base or onboarding video, consult it to see real examples that mirror the tutorial flow and tools set.
Tool Inventory and Capabilities
This section lists the tools you’ll use, third-party integrations available, limitations to keep in mind, and advice on choosing the right tool for a task.
List of included tools: Functions, DTMF handler, End Call, Transfers, Send SMS, API request tool
Vapi includes several core tools: Functions for arbitrary code execution; DTMF handlers to capture and interpret keypad input; End Call for gracefully terminating calls; Transfer tools for moving callers to external numbers or queues; Send SMS to deliver text messages after or during calls; and an API request tool to call REST services without writing custom code. Each serves a clear role in the call lifecycle.
Third-party integrations: Twilio Flows, Google Calendar, Time API
Common third-party integrations include Twilio for telephony actions (calls, SMS, transfers), Google Calendar for scheduling and event lookups, and Time APIs for timezone-aware operations. You can also integrate CRMs, ticketing systems, or analytics platforms using the API request tool or Functions. These integrations let you personalize calls, schedule follow-ups, and log interactions.
Capabilities and limits of each tool: synchronous vs asynchronous, payload sizes, response formats
Understand which tools operate synchronously (returning immediate results, e.g., DTMF capture) versus asynchronously (operations that may take longer, e.g., external API calls). Respect payload size limits for triggers and tool responses — large media or massive JSON bodies may need different handling. Response formats are typically JSON and must conform to the scenario schema. Some tools can trigger background jobs or callbacks instead of blocking the scenario; choose accordingly to avoid timeouts.
Choosing the right tool for a given voice/call task
Match task requirements to tool capabilities: use DTMF handlers to collect numeric input, Functions for complex decision-making or enrichment, API request tool for simple REST interactions, and Transfers when you need to bridge to another phone number or queue. If you need to persist data off-platform or send notifications, attach Send SMS or use Functions to write to your database. Always prefer built-in tools for standard tasks and reserve Functions for bespoke logic.
Functions Deep Dive
Functions are where you implement custom logic. This section covers their purpose, how to register them, example patterns, and best practices to keep your scenarios stable and maintainable.
Purpose of Functions in Vapi: executing code, formatting data, calling APIs
Functions let you run custom code to format data, call third-party APIs, perform lookups, and create dynamic prompts. They are your extension point when built-in tools aren’t enough. Use Functions to enrich caller context (customer lookup), generate tailored speech prompts, or orchestrate conditional branching based on external data.
How to create and register a Function with Vapi
Create a Function in your preferred runtime and implement the expected input/output contract (JSON input, JSON output with required fields). Register it in Vapi by uploading the code or pointing Vapi at an endpoint that executes the logic. Configure authentication so Vapi can call the Function safely. Add versioning metadata so you can rollback or track changes.
Example Function patterns: data enrichment, dynamic prompt generation, conditional logic
Common patterns include: data enrichment (fetch customer records by phone number), dynamic prompt generation (compose a personalized message using name, balance, appointment time), and conditional logic (if appointment is within 24 hours, route to a specific flow). Combine these to create high-value interactions, such as fetching a calendar event and then offering to reschedule via DTMF options.
Best practices: idempotency, error handling, timeouts, and logging
Make Functions idempotent where possible so retries do not create duplicate side effects. Implement robust error handling that returns structured errors to the scenario so it can branch to fallback behavior. Honor timeouts and keep Functions fast; long-running tasks should be deferred or handled asynchronously. Add logging and structured traces so you can debug failures and audit behavior after the call.
Make Scenario Walkthrough
Scenarios define the full call lifecycle. Here you’ll learn the concept, how to build one step-by-step, attach conditions, and the importance of testing and versioning.
Concept of a Scenario: defining the end-to-end call logic and tool sequence
A Scenario is a sequence of steps that represents the entire call flow — from initial greeting to termination. Each step invokes a tool or Function and optionally evaluates responses to decide the next action. Think of a Scenario as a script plus logic, where each tool is a stage in that script.
Step-by-step creation of a scenario: selecting triggers, adding tools, ordering steps
Start by selecting a trigger (incoming call, scheduled event, or API invocation). Add tools for initial greeting, authentication, intent capture, and any backend lookups. Order steps logically: greet, identify, handle request, confirm actions, and end. At each addition, map expected inputs and outputs so the next tool receives the right context.
Attaching conditions and branching logic for different call paths
Use conditions to branch based on data (DTMF input, API results, calendar availability). Define clear rules so the scenario handles edge cases: invalid input, API failures, or unanswered transfers. Visualize the decision tree and keep branches manageable to avoid complexity explosion.
Saving, versioning, and testing scenarios before production
Save versions of your Scenario as you iterate so you can revert if needed. Test locally with simulated inputs and in staging with real webhooks using sandbox numbers. Run through edge cases and concurrent calls to verify behavior under load. Only promote to production after automated and manual testing pass.
Attaching Tools to Scenarios
This section explains how to wire tools into scenario steps, pass data between them, and use practical examples to demonstrate typical attachments.
How to attach a tool to a specific step in a scenario
In the scenario editor, select the step and choose the tool to attach. Configure tool-specific settings (timeouts, prompts, retry logic) and define the mapping between scenario variables and tool inputs. Save the configuration so that when the scenario runs, the tool executes with the right context.
Mapping inputs and outputs between tools and the scenario context
Define a consistent schema for inputs and outputs in your scenario context. For example, map caller.phone to your Function input for lookup, and map Function.result.customerName back into scenario.customerName. Use transforms to convert data types or extract nested fields so downstream tools receive exactly what they expect.
Passing metadata and conversation state across tools
Preserve session metadata like call ID, start time, or conversation history in the scenario context. Pass that state to Functions and API requests so external systems can correlate logs or continue workflows. Store transient state (like current menu level) and persistent state (like customer preferences) appropriately.
Examples: attaching Send SMS after End Call, using Functions to prepare API payloads
A common example is scheduling an SMS confirmation after the call ends: attach Send SMS as a post-End Call step or invoke it from a Function that formats the message. Use Functions to prepare complex API payloads, such as a calendar invite or CRM update, ensuring the payload conforms to the third-party API schema before calling the API request tool.
Tools Format and Response Structure
Tool responses must be well-formed so Vapi can act. This section describes the expected JSON schema, common fields, how to trigger actions, and debugging tips.
Standard response schema expected by Vapi for tool outputs (JSON structure and keys)
Tool outputs typically follow a JSON schema containing keys like status, content, actions, and metadata. Status indicates success or error, content contains user-facing text or media references, actions tells Vapi what to do next (play, collect, transfer), and metadata carries additional context. Stick to the schema so Vapi can parse responses reliably.
Common response fields: status, content, actions (e.g., transfer, end_call), and metadata
Use status to signal success or failure, content to deliver prompts or speech text, actions to request behaviors (transfer to number X, end_call with summary), and metadata to include IDs or tracing info. Include action parameters (like timeout durations or DTMF masks) inside actions so they’re actionable.
How to format tool responses to trigger actions like playing audio, collecting DTMF, or transferring calls
To play audio, return an action with type “play” and either a TTS string or a media URL. To collect DTMF, return an action with type “collect” and specify length, timeout, and validation rules. To transfer, return an action type “transfer” with the destination and any bridging options. Ensure your response obeys any required fields and valid values.
Validating and debugging malformed tool responses
Validate tool outputs against the expected JSON schema locally before deploying. Use logging and simulated scenario runs to catch malformed responses. If Vapi logs an error, inspect the raw response and compare it to the schema; common issues include missing fields, incorrect data types, or oversized payloads.
Handling End Call
Ending calls gracefully is essential. This section explains when to end, how to configure the End Call tool, graceful termination practices, and testing strategies for edge cases.
When and why to use End Call tool within a scenario
Use End Call when the interaction is complete, when you need to hand off the caller to another system that doesn’t require a bridge, or to terminate a failed or idle session. It’s also useful after asynchronous follow-ups like sending SMS or scheduling an appointment, ensuring resources are freed.
Step-by-step: configuring End Call to play final prompts, log call data, and clean up resources
Configure End Call to play a closing prompt (TTS or audio file), then include actions to persist call summary to your database or notify external services. Make sure the End Call step triggers cleanup tasks: release locks, stop timers, and close any temporary resources. Confirm that any post-call notifications (emails, SMS) are sent before final termination if they are synchronous.
Graceful termination best practices: saving session context, notifying external services
Save session context and key metrics before ending the call so you can analyze interactions later. Notify external services with a final webhook or API call that includes call outcome and metadata. If you can’t complete a post-call operation synchronously, record a task for reliable retry and inform the user in the call if appropriate.
Testing End Call behavior across edge cases (network errors, mid-call errors)
Simulate network failures, mid-call errors, and abrupt disconnects to ensure your End Call step handles these gracefully. Verify that logs still capture necessary data and that external notifications occur or are queued. Test scenarios that end earlier than expected and ensure cleanup doesn’t assume further steps will run.
Conclusion
You’ve seen the main building blocks of Vapi voice automation and how to assemble them into robust scenarios. This final section summarizes next steps and encourages continued experimentation.
Summary of key steps for building Vapi scenarios with Functions, DTMF, End Call, Transfers, and API integrations
To build scenarios, prepare accounts and credentials, set up your environment with a secure secrets store, and configure Twilio and ngrok for testing. Use Functions to enrich data and format payloads, DTMF handlers to collect input, Transfers to route calls, End Call to finish sessions, and API tools to integrate external services. Map inputs and outputs carefully, version scenarios, and test thoroughly.
Recommended next steps: prototype, test, secure, and iterate
Prototype a simple scenario first (greeting, DTMF menu, and End Call). Test with sandbox and real phone numbers, secure your credentials, and iterate on prompts and branching logic. Add logging and observability so you can measure success and improve user experience. Gradually add integrations like Google Calendar and SMS to increase value.
Where to get help, how to provide feedback, and how to contribute examples or improvements
If you run into issues, consult your internal docs or community resources available in your workspace. Provide feedback to your platform team or maintainers with specific examples and logs. Contribute back by adding scenario templates or prompt examples to the Tool & Prompt Vault to help colleagues get started faster.
Encouragement to experiment with the Tool & Prompt Vault and share successful scenario templates
Experiment with the Tool & Prompt Vault to reuse effective prompts and template logic. Share successful scenario templates and Functions with your team so everyone benefits from proven designs. By iterating and sharing, you’ll accelerate delivery and create better, more reliable voice experiences for your users.
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