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

Annotations already establish readOnly, idempotent, non-destructive and open-world access, so the safety profile is covered. The description adds genuinely non-structured context: the call is free/no-payment, the transcript is truncated to ~2000 characters, and no AI analysis is performed. That cap and the absence of analysis are the kind of limitations an agent needs before choosing this over the paid tool.

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?

Front-loaded with the action and result, followed by two short lines that each carry distinct information (positioning vs. paid sibling, and the truncation/no-analysis cap). The third line is a telegraphic fragment list, which is dense but reads slightly clipped rather than fully polished.

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 shape need not be described, and the single parameter is fully documented. Combined with the cap disclosure, the no-payment fact, and the sibling routing, an agent has everything required to decide and invoke correctly.

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?

There is a single parameter and schema description coverage is 100%, so the schema already explains that video_url accepts a URL or bare video ID. The description adds nothing about accepted formats, ID-vs-URL handling, or what happens with the empty default. Baseline 3 is appropriate when the schema does all the work.

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 (fetch), a specific resource (free YouTube video preview) and enumerates the returned payload (title, channel, stats, transcript excerpt). It explicitly positions itself relative to the sibling get_video_intelligence, so an agent can tell the two apart without opening either schema.

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?

Names the alternative explicitly ('Taster for get_video_intelligence') and gives the selecting condition (use before committing to payment), which is real routing guidance. It does not address other plausible siblings such as transcript_text or transcript_markdown, so it stops short of full when/when-not coverage.

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