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

Annotations already declare readOnlyHint, idempotentHint, destructiveHint=false and openWorldHint, so the safety profile is covered. The description still adds real value beyond them: the 20 MiB ceiling and the fact that case customer, message owner and environment are re-verified on every read — an authorization behavior the annotations do not convey.

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?

Three compact sentences, with the return shape and size limit front-loaded before the sourcing hint and the authorization note. Nothing is redundant and no sentence could be removed without losing a fact.

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 correctly names the four returned fields, and it covers the size cap and per-read authorization checks. The main remaining gap is failure behavior — what an agent should expect if the attachment exceeds 20 MiB or the index is stale.

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 40%, so the description must compensate for undocumented parameters, and it largely does: it maps the `message` param to careMessageId and `index` to a preview.attachments index. The `case` parameter's role is only implied via the authorization sentence, and it never explains what happens at the 0-99 index bounds.

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 states a specific verb and resource ("Read an original care-message attachment") and enumerates the returned fields plus the 20 MiB cap, so the operation is unmistakable. It does not, however, distinguish this tool from the sibling summer_cases_attachment, leaving the agent to infer which of the two to call.

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?

"Use careMessageId and preview.attachments index from cases.get" gives concrete guidance on where the identifiers come from, which is exactly the context needed to invoke it correctly. It stops short of stating when not to use it or which sibling to prefer for the other attachment-listing case.

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