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

Annotations already declare readOnly/idempotent/non-destructive, so the safety profile is covered. The description adds meaningful context beyond that: the reporting window is the last N days and it returns a fixed metric set (views, watch time, duration, subscribers gained/lost, engagement). It does not discuss pagination or multi-channel default behavior, but with annotations carrying safety this is solid.

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?

A single dense sentence with the resource and metric list front-loaded, followed by the one non-obvious parameter rule. No filler and nothing repeated from the schema or annotations.

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?

An output schema exists, so return values needn't be explained, yet the description still lists the key metrics. Both parameters are covered. The only gap is behavior when multiple channels exist and channel is left empty, which is implied but not stated.

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%, so the description must compensate and largely does: 'last N days' gives meaning to days, and the channel guidance ('a value from youtube_channels', 'leave empty if there's only one channel') adds real semantics beyond a bare string param. The default of 28 days is not stated, keeping it short of a 5.

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?

States a specific verb+resource ('YouTube channel OVERVIEW') and enumerates the exact metrics returned, so an agent can distinguish it from youtube_top_videos and youtube_traffic_sources without opening the schema. The time scope ('last N days') is also front-loaded.

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?

Usage is implied by the metric list and the channel-selection note, but there is no explicit when-to-use guidance relative to sibling tools like youtube_channels (which the description references as a source of valid values) or youtube_top_videos. The 'leave empty if there's only one channel' hint is the only routing-style guidance.

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