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

Annotations already provide readOnlyHint=true, so the read-only nature is covered. The description adds behavioral details beyond that: it returns results newest-first, has an error path with a returned link, and respects the optional channel/since filters. It does not contradict the 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?

Three compact sentences, with the core purpose and scope front-loaded, followed by optional filters and the error-handling note. No filler or redundant phrasing.

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 search tool with no output schema, the description covers the essential operational behavior: scope, ordering, filtering options, and the error-handling case. It does not describe the exact result format (e.g., message fields), but that is reasonable given the tool's simplicity and the schema's parameter coverage.

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 the schema already explains each parameter. The description rephrases some (e.g., 'id or #name' matches the schema) but adds minimal extra meaning. It does not go beyond the schema enough to warrant a higher score, 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?

The description opens with a specific verb-resource pair ('Search the Slack messages') and adds the dual search modes (keyword and meaning) plus scope ('channels the user switched on and their DMs with YouSpot'). It is unambiguous and clearly distinct from sibling tools like get_slack_thread or list_slack_channels.

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 clearly states the scope of what is searched ('nothing outside those') and mentions the error-handling branch ('if it reports no Slack workspace connected'). However, it does not explicitly name alternatives or give a 'when not to use' condition, so it stops short of a 5.

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