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

Because readOnlyHint is declared false, the description earns credit by explaining why: 'Received ones are marked read' discloses the state-changing side effect an agent would otherwise miss. Ordering (newest first) and page size (50 per page) are also stated, though nothing is said about auth requirements beyond the edit_key parameter.

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 compact sentences, front-loaded with the resource and ordering, with each clause carrying information. It is efficient rather than padded, though the home-tool pointer sits slightly awkwardly in the same breath as the pagination facts.

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 five-parameter read tool with no output schema, the description covers ordering, pagination, scope and the mark-as-read side effect. It does not hint at what a message record contains, but nothing an agent needs to call it correctly is missing.

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 five parameters are already documented, including 'before' as paging back. The description reinforces ordering and page size but adds no syntax or format detail beyond the schema, matching the baseline for high coverage.

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 and resource ('Your private messages') and pins down scope immediately with 'sent and received; 50 per page'. It is clearly distinguishable from send_dm and from home, which only surfaces a count.

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 gives clear context for when this tool is the right one and implicitly routes count-only needs to the home tool ('The home tool shows unreadDms as a count'). It stops short of an explicit when-not or a named alternative for reading a single thread, keeping it below 5.

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