YouTube MCP

Reply to a comment

reply_to_comment

Destructive

Post a public reply to a YouTube comment thread as the connected channel; it appears immediately, notifies the original commenter, and requires confirm:true.

Instructions

Post a public reply to a comment thread as the connected channel. It is visible the moment it lands and it notifies the person you replied to, which a later delete does not undo. Needs confirm: true.

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": {
      "parent_id": "<parent_id>",
      "text": "<text>"
    },
    "name": "reply_to_comment"
  }
}

Input Schema

Name	Required	Description
`text`	Yes
`account`	No	Which connected channel to act on (name or @handle). Required when more than one is connected: without it the call fails and lists the choices rather than picking one.
`confirm`	No	Set true only when the user asked for exactly this action.
`parent_id`	Yes	The comment thread id from list_comments.

Schema Changelog

Changes observed during successful MCP inspections.

Changed3 schema fields changedv3.0.2Oct 5, 2026

removedInput schema / $schema

Removed value: -"http://json-schema.org/draft-07/schema#"

removedInput schema / additionalProperties
```
Removed value: -false
```

changedInput schema / properties / confirm / description

Previous value: -"Must be true. This posts publicly."New value: +"Set true only when the user asked for exactly this action."

First observedv1.0.0Sep 2, 2026

TDQS

A4.5/5.0

Behavior5/5

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

Annotations declare destructiveHint=true and idempotentHint=false, but the description adds consequences the annotations cannot express: the reply is public immediately, it notifies the recipient, and a later delete does not undo that notification. That is exactly the irreversibility context an agent needs before a non-idempotent write.

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?

Three tight sentences, front-loaded with the action and its visibility/notification consequences, then the confirm gate. No filler and no repetition of the schema.

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

Completeness5/5

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

For a non-idempotent, public mutation with no output schema, the description covers visibility, side effects, irreversibility, and the confirmation prerequisite, while annotations carry the safety profile. Nothing essential to correct invocation is missing.

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 coverage is 75% and the schema already documents account, confirm, and parent_id in detail; the description only restates the confirm requirement without adding format or edge-case meaning. Baseline 3 applies when the schema does the heavy lifting.

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

Purpose5/5

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

States a specific verb (post), resource (public reply), and target (comment thread), plus the acting identity (connected channel). An agent can distinguish this from list_comments and the other read-oriented siblings without opening a schema.

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?

Gives a clear operational prerequisite ('Needs confirm: true') that gates invocation, and the schema's account field reinforces the multi-channel condition. It stops short of naming alternatives or explicit when-not-to-use conditions, so it falls short of a 5.

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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