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docs: enrich dynamic variables table and document function.parameters tool support #1037

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33 changes: 21 additions & 12 deletions fern/assistants/dynamic-variables.mdx
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Expand Up @@ -69,18 +69,27 @@ For example, set the assistant's first message to "Hello, `{{name}}`!" and assig

These variables are automatically filled based on the current (UTC) time, so you don't need to set them manually in `variableValues`:

| Variable | Description | Example |
| ----------------------- | --------------------------------- | ------------------------- |
| `{{now}}` | Current date and time (UTC) | Jan 1, 2024 12:00 PM |
| `{{date}}` | Current date (UTC) | Jan 1, 2024 |
| `{{time}}` | Current time (UTC) | 12:00 PM |
| `{{month}}` | Current month (UTC) | January |
| `{{day}}` | Current day of month (UTC) | 1 |
| `{{year}}` | Current year (UTC) | 2024 |
| `{{customer.number}}` | Customer's phone number | +1xxxxxxxxxx |
| `{{customer.X}}` | Any other customer property | |
| `{{transport.conversationType}}` | Whether the conversation is over `chat` or `voice` | `chat` |
| `{{transport.X}}` | Any other transport-related property | |
| Variable | Description | Example |
| --------------------------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------ | ------------------------------------------------------ |
| `{{now}}` | Current date and time (UTC). For other timezones, use the LiquidJS `date` filter -- see [Advanced date and time usage](#advanced-date-and-time-usage) below. | Jan 1, 2024 12:00 PM |
| `{{date}}` | Current date (UTC) | Jan 1, 2024 |
| `{{time}}` | Current time (UTC) | 12:00 PM |
| `{{month}}` | Current month (UTC) | January |
| `{{day}}` | Current day of month (UTC) | 1 |
| `{{year}}` | Current year (UTC) | 2024 |
| `{{customer.number}}` | The customer's phone number (caller-ID for inbound calls, destination for outbound calls). | +1xxxxxxxxxx |
| `{{customer.X}}` | Any other customer property you set when creating the call. | |
| `{{phoneNumber.number}}` | The Vapi phone number that received the inbound call or placed the outbound call. | +1xxxxxxxxxx |
| `{{phoneNumber.name}}` | The display name you set on this phone number in the dashboard. | `Main Support Line` |
| `{{call.id}}` | The unique Vapi-generated ID for this call. Useful for correlating with your own logs, support tickets, or webhooks. | `5fe26c8e-...` |
| `{{call.type}}` | The kind of call this is. Useful for branching prompt behavior between channels. | `inboundPhoneCall` / `outboundPhoneCall` / `webCall` |
| `{{transport.callSid}}` | The provider-side call session ID (e.g. Twilio's `CallSid`). Useful for BYOT customers correlating with their own provider logs. | `CA1234...` |
| `{{transport.conversationType}}` | Whether the conversation is over `chat` or `voice`. | `chat` |
| `{{transport.X}}` | Any other transport-related property. | |

<Note>
To pass these values **between tool calls within an assistant** (rather than templating them into prompts), see [Static variables and aliases](/tools/static-variables-and-aliases). That page documents the trust tiers for these variables -- which are signaling-derived and safe to use as a security boundary in tool calls, vs. conversation-derived ones that are not -- and shows how to inject them into tool calls deterministically, without LLM mediation.
</Note>

## Advanced date and time usage

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14 changes: 14 additions & 0 deletions fern/tools/custom-tools.mdx
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Expand Up @@ -119,6 +119,20 @@ vapi listen --forward-to localhost:3000/tools/webhook
`vapi listen` is a local forwarder that requires a separate tunneling service. Configure your tool's server URL to use the tunnel's public URL for testing. [Learn more →](/cli/webhook)
</Note>

## Other tool types that accept custom function parameters

Custom function tools are not the only tool type where you can define an LLM-facing JSON schema. Several other tool types accept the same `function.parameters` customization, so the dashboard's **Parameters** editor (or the `function` field in the API) works the same way across them.

| Tool type | Customer-defined `function.parameters`? |
| ------------------------------------------------------------------------------------------------------------------------------------------------------------------------ | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ |
| `function` (custom) | Yes — the entire purpose of this tool type. |
| `apiRequest` | Yes — drives both the LLM-supplied arguments and the request body construction. |
| `code` | Yes — the parameters become inputs to your TypeScript code. |
| `handoff` | Yes — fills handoff-time arguments inline. See [Approach 1 in the squads guide](/squads/passing-data-between-assistants#approach-1-handoff-arguments). |
| `transferCall`, `endCall`, `dtmf`, `voicemail`, `sms`, `slack-send-message`, GHL/Google integrations, `mcp`, `make`, Anthropic-native (`bash`, `computer`, `textEditor`) | No — the schema is Vapi-controlled or auto-derived from the underlying integration; you do not define it directly. |

For tool types that accept customer-defined `function.parameters`, you can also pair them with **static parameters** -- a separate top-level `parameters` array on the tool that merges server-trusted values into the body without the LLM ever seeing them. See [Static variables and aliases](/tools/static-variables-and-aliases) for the full pattern, including when to use static parameters as a security boundary.

## Alternative: API Configuration

For advanced users who prefer programmatic control, you can also create and manage tools via the Vapi API:
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