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

Annotations already declare readOnlyHint=true, destructiveHint=false and openWorldHint=false, so the safety profile is covered. The description adds one genuinely useful behavioral fact beyond that — a 90-day retention window — but never says how the file comes back (URL vs. bytes) or any size/type limits, which matters for a fetch 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?

Two short sentences, zero filler, with the resource scope front-loaded and the dependency noted parenthetically. Nothing could be cut without losing information.

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 carries the burden of explaining the return value, and it does not — an agent cannot tell whether it receives a media URL, a base64 payload, or a reference. Retention is covered, but the return contract is not.

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%, so all three parameters including brand and contact are already documented in structured form. The description only restates the id-to-read_chat mapping and adds no new semantics, so the baseline 3 applies.

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) and a concrete resource set (photo, voice note, video, document) scoped to chats, which is clearly distinct from sibling read_chat and list_chats. It doesn't explicitly name a sibling to contrast with, but the resource type alone makes the split obvious.

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?

Implies the workflow by tying the required id to 'read_chat', so an agent understands this is a second step after reading a message. However, there is no explicit when-to-use/when-not, no mention of what to do if the file is expired, and no stated alternatives.

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