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

Annotations already cover readOnlyHint, idempotentHint, and openWorldHint. The description adds useful behavioral detail: own messages are excluded and mentions are included, and authentication is required. It does not clarify whether the optional mark_read parameter causes any state change, which matters for a tool annotated as read-only.

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 compact and front-loads the core behavior before the authentication note. Every phrase carries meaning, though the sentence fragment and trailing ellipsis reduce polish slightly.

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 annotations covering safety, the core semantics and auth requirement are present. However, with no output schema and zero schema description coverage, the description should explain the return format and the role of mark_read; those gaps leave it only minimally adequate.

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 0%, so the description must compensate. It only partially explains 'key' via 'Needs key or sign-in' and gives no explanation of the 'mark_read' parameter at all, leaving half the parameters semantically undocumented.

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 resource and scope: per-space unread messages by others since the last read, plus mentions of the user. It also clarifies that the user's own messages never count. It does not explicitly distinguish itself from siblings like space_read or space_context, so it falls short of a 5.

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?

Usage is implied as checking unread/mention status, and the description adds the prerequisite 'Needs key or sign-in.' However, it gives no explicit when-to-use vs when-not guidance and does not name alternatives such as space_read or spaces_mine.

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