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

Annotations already establish this as a safe, read-only, idempotent call, so the bar is lower; the description still adds real value by disclosing that no API key is needed and that returned download URLs are temporary. The temporary-URL caveat is exactly the kind of behavior an agent cannot infer from the annotations. It does not describe rate limits or how many formats are typically returned.

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?

Four short sentences, with the core purpose front-loaded and the constraints following in descending importance. The closing permission/legal sentence is arguably boilerplate for tool-selection purposes, but nothing is padded or redundant.

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?

With an output schema present, the description need not explain return values, and it correctly focuses on scope, auth posture, and URL temporality. The one gap is that it never positions itself relative to 'prepare_social_media_download', which shares the download workflow and would need disambiguation in a 23-tool list.

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 description coverage is 100% and the mode enum with its 'both' default is fully documented in the schema, so the description does no parameter work at all. Per the calibration rule, a 100%-covered two-parameter schema establishes a baseline of 3.

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 ('Get') and resource ('MP4 and MP3 download options') and narrows scope to public YouTube, Instagram, or TikTok URLs. It is clear on its own, but it never distinguishes itself from the sibling 'prepare_social_media_download', which an agent will likely need to choose between.

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?

It states a usable condition ('public tool does not require a dopost API key') and an implicit constraint (URLs must be public, from one of three platforms), which is helpful. However there is no when-to-use versus when-not-to-use guidance and no routing to the closely related 'prepare_social_media_download' sibling, leaving the selection decision to inference.

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