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

Annotations already declare readOnlyHint=true, so the safety profile is covered. The description adds real context beyond that: a 5MB ceiling and the fact that the Chatwork-issued URL is fetched over an SSRF-pinned, validated-public-address path — meaningful for an agent reasoning about failure modes and security behavior.

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 tight sentences with zero filler; the core action and its size limit come first, with the SSRF detail as supporting context.

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?

A read-only tool with fully documented parameters and no output schema, and the description still declares the return encoding (base64). What is missing is minor: how oversized files fail and whether binary content is truncated.

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 room_id, file_id, and account are all documented in the schema. The description adds nothing about parameter formats or the multi-account disambiguation rule, so 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 (download) and resource (one file posted in a Chatwork room), plus the output encoding (base64) and a size ceiling. The Chatwork scope distinguishes it from siblings like read_slack_file or download_attachment, though it never names an alternative explicitly.

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 5MB limit implies a constraint but the description gives no when-to-use guidance, no prerequisites, and no routing against the many nearby read/download siblings (read_file_content, download_file_content, read_slack_file). Usage must be inferred from the resource name.

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