Phone Bud

Update a voice agent

update_agent

DestructiveIdempotent

Update an existing voice agent. Only the fields you provide change. Custom agents are fully editable; 'alex' and 'digital_twin' template agents are server-managed — only name, voice (alex only), and is_favorite apply to those.

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": {
      "agent_id": "<agent_id>"
    },
    "name": "update_agent"
  }
}

Input Schema

Name	Required	Description
`name`	No	New agent name.
`speed`	No	Speaking-rate multiplier (Fish prosody.speed): 1.0 = normal, below 1 slower, above 1 faster. Clamped to 0.5–2.
`voice`	No	Preset voice name — Wesley (American male, warm and friendly), Grant (American male, polished), Beau (American male, laid-back), Bobby (Southern US male, relaxed), Sheila (American female, young and natural), Harper (American female, crisp and professional), Beulah (Southern US female, older and friendly), Avery (Canadian female, clear and friendly), Megan (British female (London), warm and relaxed), Sophia (British female, professional), Oliver (British male, clear and professional), Hamish (Scottish male, older and warm), Cathal (Irish male, warm and gentle), Chloe (Australian female, clear and confident), Dean (Australian male, friendly), Priya (Indian female, clear and professional), Rohan (Indian male, clear and confident), Lerato (South African female, confident), Amara (Nigerian female, clear and confident), Karanja (Kenyan male, upbeat) — or a 32-character Fish Audio reference id.
`agent_id`	Yes	Agent UUID (see list_agents).
`greeting`	No	New default greeting (custom agents only).
`tts_model`	No	Fish TTS model: 's1' (stable) or 's2-pro' (higher quality).
`description`	No	New description (custom agents only).
`is_favorite`	No	Whether this is the default agent.
`temperature`	No	Deprecated and ignored: the call LLM's sampling is set server-wide.
`system_prompt`	No	New persona / standing instructions (custom agents only).
`background_sound`	No	The room the agent seems to call from, a quiet sound under its voice. 'none' is a silent line. Default: 'office'.

Schema Changelog

Changes observed during successful MCP inspections.

First observedNov 10, 2026

TDQS

A4/5.0

Behavior4/5

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

Annotations already declare destructiveHint=true and idempotentHint=true, so the safety profile is covered. The description adds genuinely new behavior: partial-update semantics and the server-managed restriction on template agents, which the annotations cannot convey. It stops short of explaining what 'destructive' means here (overwriting existing field values).

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 sentences, zero waste, with the core update semantics front-loaded and the template-agent caveat following. Every clause carries information an agent needs.

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

Completeness4/5

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

For an 11-parameter mutation tool with full schema coverage and no output schema, the description covers the two things the schema cannot: partial-update behavior and template-agent field restrictions. It could say more about failure modes (invalid agent_id, rejected fields on templates), but it is largely complete.

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?

Schema description coverage is 100%, so the schema already documents every parameter, including the deprecated temperature and the voice list. The description adds the meaningful cross-parameter rule that only supplied fields change and that most fields are ignored for template agents, but per-parameter meaning is left to the schema. Baseline 3 is appropriate.

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?

States a specific verb and resource ('Update an existing voice agent') and immediately distinguishes custom agents from server-managed template agents ('alex', 'digital_twin'). It does not name a sibling like create_agent, but the agent-type split gives enough to identify the tool's role.

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?

Explicitly states partial-update semantics ('Only the fields you provide change') and the condition under which fields are ignored (template agents: only name, voice for alex, and is_favorite apply). It lacks an explicit 'use create_agent instead for new agents' routing, but the context is 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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