stephenvapiai · Sep 28, 2026 · Sep 25, 2026 · Sep 25, 2026
diff --git a/fern/assistants/examples/appointment-scheduling.mdx b/fern/assistants/examples/appointment-scheduling.mdx
@@ -97,7 +97,7 @@ Use sample CSVs for customers, services, and appointments during development.
 
 ## 2. Create calendar tools
 
-Use the Google Calendar integration for availability and booking, or your own API via a custom tool.
+Use the Google Calendar integration for availability and booking, or your own API via a Function tool.
 
 <Tabs>
   <Tab title="Use Google Calendar (recommended)">
@@ -109,10 +109,10 @@ Use the Google Calendar integration for availability and booking, or your own AP
     - `reschedule_appointment(appointmentId, time)`
     - `cancel_appointment(appointmentId)`
   </Tab>
-  <Tab title="Custom tools (HTTP)">
+  <Tab title="Function tools (HTTP)">
     See: [Function tools](/tools/custom-tools)
 
-    Define function tools that call your scheduling backend. Attach CSV knowledge bases (customers/services) if using the sample data above.
+    Define Function tools that call your scheduling backend. Attach CSV knowledge bases (customers/services) if using the sample data above.
   </Tab>
 </Tabs>
 

diff --git a/fern/assistants/examples/lead-qualification.mdx b/fern/assistants/examples/lead-qualification.mdx
@@ -67,7 +67,7 @@ Create an outbound sales assistant that calls prospects, qualifies them using BA
 
 ## 2. Create sales tools
 
-Configure function tools or your CRM API for:
+Configure Function tools or your CRM API for:
 - `lookup_lead(leadId)`
 - `score_lead(budget, authority, need, timeline)`
 - `update_crm(leadId, callOutcome, nextSteps)`
@@ -169,4 +169,3 @@ Create a phone number or trigger an outbound call. See [Phone calls](/quickstart
 - **CRM integration**: Connect your CRM via [Function tools](/tools/custom-tools)
 - **Calendar**: [Google Calendar](/tools/google-calendar)
 - **Escalation**: Use a [Squad](/squads) to hand off to a specialized closer
-
diff --git a/fern/calls/call-dynamic-transfers.mdx b/fern/calls/call-dynamic-transfers.mdx
@@ -32,7 +32,7 @@ For a lookup that chooses among predefined branch or department phone numbers, f
 Dynamic transfers with live call control use a server-controlled pattern that gives you maximum flexibility:
 
 1. **User initiates transfer**: The user requests a transfer in natural language during the conversation
-2. **Vapi triggers custom tool**: Vapi fires your custom tool to your HTTP server
+2. **Vapi triggers a Function tool**: Vapi sends the Function tool request to your HTTP server
 3. **Server receives control URL**: The tool payload includes `message.call.monitor.controlUrl` for live call control
 4. **Execute business logic**: Your server performs any necessary operations:
    - Update CRM records with call summaries
@@ -45,7 +45,7 @@ Dynamic transfers with live call control use a server-controlled pattern that gi
 Available context: Your server receives the full conversation transcript, custom parameters, call metadata, and the control URL, allowing you to make informed routing decisions and execute the transfer programmatically.
 
 <Tip>
-Parameters for custom tools are fully customizable. You can name and structure them however you like to guide routing (for example `department`, `reason`, `urgency`, `customerId`, etc.).
+Function tool parameters are fully customizable. Name and structure them to guide routing (for example, `department`, `reason`, `urgency`, or `customerId`).
 </Tip>
 
 Sequence diagram
@@ -78,14 +78,14 @@ sequenceDiagram
 ## Quick Implementation Guide
 
 <Steps>
-  <Step title="Create a custom tool for dynamic transfers">
-    Create a custom tool that will receive the transfer request and provide you with the control URL to execute the transfer.
+  <Step title="Create a Function tool for dynamic transfers">
+    Create a Function tool that will receive the transfer request and provide you with the control URL to execute the transfer.
 
     <Tabs>
       <Tab title="Dashboard">
         - Navigate to **Tools** in your dashboard
         - Click **Create Tool** 
-        - Select **Custom** as the tool type
+        - Select **Function tool** as the tool type
         - Set function name: `transfer_call`
         - Add a description: "Transfer the call to the appropriate department or agent"
         - Define custom parameters based on your routing needs (e.g., `department`, `reason`, `urgency`, `customerId`)
@@ -226,7 +226,7 @@ sequenceDiagram
       <Tab title="Dashboard">
         - Navigate to **Assistants** 
         - Create a new assistant or edit an existing one
-        - Add your custom transfer tool to the assistant
+        - Add your `transfer_call` Function tool to the assistant
         - Configure the system prompt to guide when transfers should occur
       </Tab>
       <Tab title="TypeScript (Server SDK)">
@@ -564,7 +564,7 @@ sequenceDiagram
 
 ## Troubleshooting
 
-- **Tool call not received**: Verify your server URL is correctly configured in the custom tool and is publicly accessible. Check your server logs for incoming requests.
+- **Tool call not received**: Verify your server URL is correctly configured in the Function tool and is publicly accessible. Check your server logs for incoming requests.
 - **Transfer not executing**: Make sure that you are sending a valid destination object (type number or sip). See API reference [here](https://docs.vapi.ai/api-reference/tools/create#request.body.TransferCallTool.destinations).
 - **Invalid destination format**: For phone numbers, use `"type": "number"` with E.164 format. For SIP, use `"type": "sip"` with a valid SIP URI.
 - **Transfer fails silently**: Check your server logs for errors in the axios/httpx request.
@@ -573,4 +573,4 @@ sequenceDiagram
 
 * **[Transfer Call tool](/tools/transfer-call)** - Static transfer options and transfer plans
 * **[Webhooks](/server-url)** - Webhook security and event handling patterns
-* **[Function tools](/tools/custom-tools)** - Build function tools for advanced routing logic
+* **[Function tools](/tools/custom-tools)** - Build Function tools for advanced routing logic
diff --git a/fern/calls/call-handling-with-vapi-and-twilio.mdx b/fern/calls/call-handling-with-vapi-and-twilio.mdx
@@ -261,7 +261,7 @@ app.listen(3000, () => {
 
 ## Note on Replacing "Connect" with Vapi Tools
 
-Vapi offers built-in functions or custom tool calls for placing a second call or transferring, you can replace the manual `/connect` call with that Vapi functionality. The flow remains the same: user is put in a Twilio conference, the specialist is dialed, and any no-answer events are handled.
+Vapi offers built-in functions or Function tool calls for placing a second call or transferring, you can replace the manual `/connect` call with that Vapi functionality. The flow remains the same: user is put in a Twilio conference, the specialist is dialed, and any no-answer events are handled.
 
 ## Notes & Limitations
 

diff --git a/fern/cli/mcp-integration.mdx b/fern/cli/mcp-integration.mdx
@@ -287,7 +287,7 @@ The Vapi MCP server provides these tools to your IDE:
   <Card title="Implementation Guides" icon="map">
     Step-by-step guides for complex features
 
-    **Example:** "Custom tool implementation guide"
+    **Example:** "Function tool implementation guide"
   </Card>
 </CardGroup>
 

diff --git a/fern/cli/overview.mdx b/fern/cli/overview.mdx
@@ -131,7 +131,7 @@ Everything you can do in the dashboard, now in your terminal:
 - **Phone numbers**: Purchase, configure, and manage phone numbers
 - **Calls**: Make outbound calls and view call history
 - **Campaigns**: Create and manage AI phone campaigns at scale
-- **Tools**: Configure custom functions and integrations
+- **Tools**: Configure Function tools and integrations
 - **Webhooks**: Set up and test event delivery
 - **Logs**: View system logs, call logs, and debug issues
 

diff --git a/fern/docs.yml b/fern/docs.yml
@@ -873,20 +873,14 @@ navigation:
                     path: providers/voice/inworld.mdx
                   - page: LMNT
                     path: providers/voice/imnt.mdx
-                  - page: Microsoft
-                    path: providers/voice/microsoft.mdx
                   - page: MiniMax
                     path: providers/voice/minimax.mdx
                   - page: Neuphonic
                     path: providers/voice/neuphonic.mdx
                   - page: OpenAI
                     path: providers/voice/openai.mdx
-                  - page: PlayHT
-                    path: providers/voice/playht.mdx
                   - page: RimeAI
                     path: providers/voice/rimeai.mdx
-                  - page: Sesame
-                    path: providers/voice/sesame.mdx
                   - page: Smallest AI
                     path: providers/voice/smallest-ai.mdx
                   - page: WellSaid
@@ -1109,6 +1103,12 @@ navigation:
   - tab: changelog
 
 redirects:
+  - source: /providers/voice/microsoft
+    destination: /providers/voice/overview
+  - source: /providers/voice/playht
+    destination: /providers/voice/overview
+  - source: /providers/voice/sesame
+    destination: /providers/voice/overview
   - source: /providers/gpt-live
     destination: /gpt-live/overview
   - source: /gpt-live/quickstart

diff --git a/fern/gpt-live/configuration.mdx b/fern/gpt-live/configuration.mdx
@@ -53,7 +53,7 @@ Call endCall when the caller asks to finish.
 ```
 </Step>
 <Step title="Add the tools">
-Create a function tool named `lookupAvailability` with the description “Check available appointment slots. Does not reserve or book a slot.” Add these required arguments:
+Create a Function tool named `lookupAvailability` with the description “Check available appointment slots. Does not reserve or book a slot.” Add these required arguments:
 
 | Argument | Type | Description |
 | --- | --- | --- |
@@ -62,7 +62,7 @@ Create a function tool named `lookupAvailability` with the description “Check
 
 Set the tool's Server URL to your HTTPS handler.
 
-Attach the function tool and an `endCall` tool to the assistant. You can also create a saved tool through [Create Tool](/api-reference/tools/create) and select it in the dashboard.
+Attach the Function tool and an `endCall` tool to the assistant. You can also create a saved tool through [Create Tool](/api-reference/tools/create) and select it in the dashboard.
 </Step>
 <Step title="Set the greeting and publish">
 Set the first message to “Hello. I can check appointment availability. What date and time zone should I check?” and configure the assistant to speak first.

diff --git a/fern/issue-reporting.mdx b/fern/issue-reporting.mdx
@@ -132,10 +132,10 @@ For problems with the Vapi dashboard interface, configuration screens, or any vi
 URL: https://dashboard.vapi.ai/assistants/create
 Browser: Chrome 120.0.6099.109
 OS: macOS 14.1
-Issue: Save button becomes unresponsive after adding custom tools
+Issue: Save button becomes unresponsive after adding Function tools
 Steps to reproduce:
 1. Navigate to assistant creation page
-2. Add 3+ custom tools
+2. Add 3+ Function tools
 3. Click Save - button grays out but doesn't save
 Console errors: TypeError: Cannot read property 'id' of undefined
 Screen recording: [link to recording]

diff --git a/fern/observability/evals-advanced.mdx b/fern/observability/evals-advanced.mdx
@@ -1045,7 +1045,7 @@ Use a non-empty-response check only to diagnose basic setup. Then restore the ch
 {" "}
 
 <Card title="Tools documentation" icon="wrench" href="/tools/custom-tools">
-  Build custom tools and test their behavior
+  Build Function tools and test their behavior
 </Card>
 
   <Card

diff --git a/fern/observability/evals-quickstart.mdx b/fern/observability/evals-quickstart.mdx
@@ -1362,7 +1362,7 @@ for guidance on turning real failures into regression coverage.
 {" "}
 
 <Card title="Tools documentation" icon="wrench" href="/tools/custom-tools">
-  Build custom tools and validate their behavior
+  Build Function tools and validate their behavior
 </Card>
 
   <Card

diff --git a/fern/observability/simulations-advanced.mdx b/fern/observability/simulations-advanced.mdx
@@ -43,7 +43,7 @@ During a simulation, the [**assistant**](/assistants) or [**squad**](/squads) un
 
 On the review step, open **Tool mocks & webhooks**. Under **Tool mocks**, select **Add**, then configure each mock with three fields:
 
-- **Tool**: Select one of the [**tools**](/tools) configured on the assistant or squad. Only its configured tools, including [**function tools**](/tools/custom-tools), can be mocked.
+- **Tool**: Select one of the [**tools**](/tools) configured on the assistant or squad. Only its configured tools, including [**Function tools**](/tools/custom-tools), can be mocked.
 - **Mock result**: Enter the string returned in place of the tool's live output.
 - **Enabled**: Toggle the mock on or off. A disabled mock is ignored, and the tool runs live.
 

diff --git a/fern/providers/voice/microsoft.mdx b/fern/providers/voice/microsoft.mdx
diff --git a/fern/providers/voice/overview.mdx b/fern/providers/voice/overview.mdx
@@ -19,13 +19,10 @@ The provider string is the exact value you pass in `voice.provider`.
 | [Hume](/providers/voice/hume#text-to-speech) | `hume` |
 | [Inworld](/providers/voice/inworld#text-to-speech) | `inworld` |
 | [LMNT](/providers/voice/imnt#text-to-speech) | `lmnt` |
-| [Microsoft](/providers/voice/microsoft#text-to-speech) | `microsoft` |
 | [MiniMax](/providers/voice/minimax#text-to-speech) | `minimax` |
 | [Neuphonic](/providers/voice/neuphonic#text-to-speech) | `neuphonic` |
 | [OpenAI](/providers/voice/openai#text-to-speech) | `openai` |
-| [PlayHT](/providers/voice/playht#text-to-speech) | `playht` |
 | [Rime AI](/providers/voice/rimeai#text-to-speech) | `rime-ai` |
-| [Sesame](/providers/voice/sesame#text-to-speech) | `sesame` |
 | [Smallest AI](/providers/voice/smallest-ai#text-to-speech) | `smallest-ai` |
 | [WellSaid](/providers/voice/wellsaid#text-to-speech) | `wellsaid` |
 | [xAI](/providers/voice/xai#text-to-speech) | `xai` |
-Original file line number
+Diff line change
@@ Expand Up @@
     {" "}
     <Card title="Tools documentation" icon="wrench" href="/tools/custom-tools">
-      Build custom tools and test their behavior
+      Build Function tools and test their behavior
     </Card>
       <Card
@@ Expand Down @@