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

Annotations already declare readOnly, idempotent, non-destructive, closed-world behavior, so safety is covered. The description adds genuinely new context beyond that: the return is base64-encoded media plus metadata, and the call fails unless the target message is a media message. It omits size/timeout limits for large media, which would matter for base64 payloads.

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?

Purpose and return format are front-loaded, followed by the precondition and a compact example. There is minor redundancy between 'Get message_id from query results' and the schema's own '(from query results)' note, but no wasted sentences.

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 fields, and annotations plus a 100%-covered schema handle safety and parameters. The stated media precondition and ID provenance close the main gaps; only edge cases like oversized media handling are unaddressed.

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 100%, so the baseline is 3, but the description goes further by explaining where message_id comes from and providing a concrete example with a realistic ID format ('true_123@c.us_3EB0...') that the schema's abstract string type does not convey. target_session is left to the schema only.

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 (Download) and resource (media content from a WhatsApp message), and enumerates the media kinds covered (image, video, audio, document, sticker), which no sibling tool overlaps with. An agent can identify the right tool without opening the 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?

Gives a clear precondition ('The message must be a media message') and routes the agent to the source of the ID ('Get message_id from query results'), naming the `query` sibling as the prerequisite step. It does not state when NOT to use it (e.g., non-media messages, or when only metadata is needed), 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.