subscribe_to_channel

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

With no annotations, the description carries the full burden for behavioral disclosure. It mentions the mutation (subscribe), auth context ('authenticated user'), and input validity ('must be valid and existing'). However, it does not disclose idempotency (duplicate subscriptions), required OAuth scopes, rate limits, or side effects, leaving notable gaps for a write operation.

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

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

The description is structured with clear sections (description, Args, Returns) and remains concise. It front-loads the core purpose and then adds parameter/return details. Minor redundancy ('must be valid and existing' adds little) but its length is appropriate for the content.

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

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

For a single-parameter subscription tool, the description covers the purpose, the parameter, and the return shape. It lacks edge-case behaviors (duplicate subscriptions, permission errors) but the output schema (if present) is not shown, and the description itself provides sufficient context for straightforward invocation. The mention of 'authenticated user' sets expectations.

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

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

Schema coverage is 0% (only a raw string field), and the description compensates effectively by explaining channel_id as a 'Unique identifier (ID) of the YouTube channel to subscribe to (typically starts with 'UC')'. This adds meaningful semantic detail beyond the schema, including a useful format hint.

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

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

The description uses a specific verb+resource construction ('Subscribes the authenticated user to a specified YouTube channel') and clearly differentiates from siblings like list_user_subscriptions (listing vs. subscribing) and search_youtube (finding vs. subscribing). It also specifies the exact identifier type (channelId).

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

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

The description provides no guidance on when to use this tool versus alternatives such as list_user_subscriptions or get_channel_id_by_handle. It implies usage ('subscribe to a channel') but does not state prerequisites beyond having a valid channel ID, which is a constraint rather than usage direction.

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