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

Annotations declare readOnlyHint=true and idempotentHint=true. The description adds meaningful context beyond these: it mentions that extraction happens 'on first read' and caches the result, and lists possible return statuses ('ready', 'skipped', 'failed', 'not_found') with reasons. This helps the agent understand caching behavior and failure modes, going beyond the structured annotations.

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 description is two sentences: the first states purpose and scope, the second covers behavior and usage. It is front-loaded, information-dense, and contains no redundant or filler content.

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?

For a simple read tool with one parameter, an output schema, and safety annotations, the description is complete. It covers the purpose, the caching behavior, the possible return statuses, and the exact scenario when to use it. No significant gaps remain.

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% for the single attachmentId parameter, and the schema already explains it as 'The attachment ID from the message attachments list'. The tool description adds no further parameter semantics, so baseline 3 is appropriate.

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 the specific verb 'Read' and identifies the resource as 'text/Markdown content of a file attached to a Workroom thread or sent by a customer', with file types (PDF, image, or document). This clearly distinguishes it from sibling tools like get_conversation_messages, which focuses on entire messages.

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?

The description explicitly states 'Use when a message references an attachment you need to read', providing a clear trigger condition. It does not mention when not to use or name alternative tools, so it misses the 'when-not/alternatives' criterion for a 5.

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