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

Beyond readOnlyHint/openWorldHint, it discloses result ordering (newest first), matching semantics (case-insensitive), coverage limits (only readable conversations, only the kept window), and a prompt-injection caution about message text. This is exactly the context annotations cannot carry.

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?

Front-loaded with the verb, scope, and safety note, then a compact parameter clause. Dense but nearly every clause carries operational information; it is slightly long, with the injection warning competing with the search semantics for attention.

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?

An output schema exists, so return values need not be described. For a 6-param, zero-annotation-detail read tool, the description covers ordering, coverage caveats, cross-tool routing, and safety, leaving nothing an agent needs missing before calling it.

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 coverage is 0%, so the description must compensate, and it does: `text` case-insensitivity, `channel` name/#/id forms, `sender` name/handle/id/'me', `since` accepting ISO or unix seconds, and `in_thread` true/false semantics. Only `limit` is left 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?

States a specific verb ('Search') and resource ('Slack messages Keeploop keeps on this Mac'), plus the scope boundary (read only; nothing can be posted). This clearly separates it from search_messages, search_mail, search_whatsapp, and list_slack_channels without opening any schema.

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?

Gives clear usage context: read `visibility` before concluding nothing was said, and route thread_ts/channel_id to get_slack_thread for thread contents. It does not explicitly contrast with list_slack_channels or search_messages, so the alternative-selection guidance is strong but not exhaustive.

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