CallMCP — Phone Call MCP Server

Request Human Approval

request_human_approval

Destructive

Ask a named principal for a specific decision using the provisioned voice approval channel. Requires restricted approvals:write, a configured callback host and signing secret. Returns dispatch status; the signed callback carries the decision and evidence. No approval is implied by dispatch. SMS-only delivery is unavailable.

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": {
      "source": "<source>",
      "source_request_id": "<source_request_id>",
      "principal_id": "<principal_id>",
      "channel": "<channel>",
      "summary": "<summary>",
      "risk_level": "<risk_level>",
      "expires_at": "<expires_at>",
      "callback_url": "<callback_url>"
    },
    "name": "request_human_approval"
  }
}

Input Schema

Name	Required	Description
`source`	Yes	Lowercase control-plane slug, e.g. "zehrava-gate".
`channel`	Yes
`summary`	Yes
`expires_at`	Yes
`message_id`	No
`risk_level`	Yes
`callback_url`	Yes	Must be https and host-allowlisted.
`principal_id`	Yes
`required_factors`	No
`responds_to_hash`	No
`source_intent_id`	No
`source_request_id`	Yes
`callback_secret_id`	No

Schema Changelog

Changes observed during successful MCP inspections.

First observedNov 12, 2026

TDQS

A3.8/5.0

Behavior5/5

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

Beyond the annotations, the description discloses important behavior: prerequisite permissions and configuration, dispatch status return semantics, asynchronous signed callbacks carrying the decision and evidence, and the caveat that dispatch alone does not imply approval. It also states the SMS-only channel limitation, which is valuable operational context.

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?

The description is compact and front-loaded, beginning with the core action before moving to prerequisites, return behavior, and constraints. Every sentence contributes useful context without repetition or filler.

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

Completeness2/5

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

For a complex tool with 13 parameters, 8 required fields, low schema description coverage, and no output schema, the description is incomplete. It explains the approval workflow and callback behavior well, but it does not adequately document the required input fields an agent must supply.

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

Parameters2/5

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

Schema description coverage is only 15% for 13 parameters, and the description explains only a few of them: the principal, the voice channel, and callback-related requirements. It leaves most required parameters, including risk_level, expires_at, summary, source, and source_request_id, without meaningful semantic guidance.

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 a specific verb and resource: asking a named principal for a decision through the voice approval channel. It is distinguishable from generic request tools, but it does not explicitly compare itself against sibling request tools, so it falls short of a 5.

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

Usage Guidelines4/5

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

It gives clear usage context with prerequisites: restricted approvals:write, a configured callback host, and a signing secret. It also excludes SMS-only delivery and notes that dispatch does not imply approval, though it does not explicitly say when to choose this tool over sibling approval or request tools.

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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