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vapi-mcp

vapi-mcp

by BlaineHeffron
OverviewSchemaSourceRelated ServersDiscussionsAdmin
TypeScript
Local

Apply Vapi answering template

apply_template
DestructiveIdempotent

Update a Vapi assistant by rendering a local template with client settings, applying optional overrides through deep merging.

Instructions

Render a local template with the client's settings and PATCH the existing Vapi assistant. Optional overrides are deep-merged last.

Tool call template

Replace each placeholder with a value matching the input schema. Only required parameters are included; add optional parameters as needed.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {
      "clientSlug": "<clientSlug>"
    },
    "name": "apply_template"
  }
}

Input Schema

NameRequiredDescriptionDefault
clientSlugYesStable local client slug: lowercase letters, digits, and internal hyphens
templateIdNo
assistantOverridesNoRaw JSON object matching the relevant Vapi REST request union

Schema Changelog

Changes observed during successful MCP inspections.

  1. First observedv0.1.0

TDQS

A3.7/5.0
Behavior4/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Annotations already declare destructiveHint, idempotentHint, and openWorldHint. The description adds valuable behavioral context: it explains the PATCH operation, the deep-merge last behavior for overrides, and the rendering of a local template. It does not contradict the annotations; rather, it enriches them with implementation details.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness5/5

Is the description appropriately sized, front-loaded, and free of redundancy?

Two concise sentences front-load the primary purpose and follow with the key behavioral nuance. No filler or redundant repetition of the title or schema. Every word adds value.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness3/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

With no output schema, the description does not mention return values or error behavior. It also omits prerequisites (e.g., that the assistant must already exist), though the phrase 'existing Vapi assistant' hints at it. Annotations cover idempotency and destructiveness, but for a mutation tool, additional context on side effects (e.g., what changes are persisted) would improve completeness.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters3/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

The schema covers 67% of parameters with descriptions. The description clarifies the deep-merge semantics for assistantOverrides, which adds meaning beyond the schema's vague reference to a 'Vapi REST request union'. However, templateId remains unexplained, and clientSlug's description is already sufficient. Partial compensation for the coverage gap, but not complete.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose4/5

Does the description clearly state what the tool does and how it differs from similar tools?

The description clearly states the action (render and PATCH) and the resource (existing Vapi assistant). It goes beyond the title by specifying the local template and client settings, making the purpose concrete. However, it does not explicitly contrast with sibling tools like provision_client, so it stops short of full differentiation.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines3/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

The description implicitly conveys when to use the tool (when you need to apply a template to an existing assistant), but it never states explicit conditions, exclusions, or alternatives. Given the sibling set includes related tools, explicit guidance would help, but the implication is reasonably clear.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

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