download_media

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

Annotations already declare readOnlyHint=true and openWorldHint=true, so safety is covered. The description adds genuinely new context beyond them: the return payload is base64-encoded media plus metadata, and the input must reference a media message. It omits size limits or rate limits, so it stops short of a 5.

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 what/return/precondition are front-loaded in three short lines, and the example is compact and directly actionable. The example largely repeats the schema's required fields, so it earns slightly less than full marks.

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 no output schema, the description usefully discloses the return format (base64 data + metadata) and the media-only precondition. Combined with annotations and a fully described 3-parameter schema, an agent has what it needs, though routing behavior for target_session remains unexplained.

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 both required parameters are already documented in the schema. The description restates that message_id comes from query results but says nothing about target_session or the multi-account routing behavior, so it adds little beyond the schema baseline.

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 gives a specific verb (Download) and resource (media content) and enumerates the media kinds covered (image, video, audio, document, sticker). No sibling tool competes in this domain, so an agent can route here unambiguously.

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 clear precondition ('The message must be a media message') and tells the agent where message_id comes from ('from query results'), which links to the query sibling. It does not name an alternative for non-media messages, but the trigger condition is explicit.

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