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

Annotations flag destructiveHint=true and idempotentHint=true but do not say what is destroyed; the description supplies exactly that — companyIds replaces the entire list, so omitted brands are dropped, and it tells the agent to re-include keepers. It also discloses downstream effects on the home view and offer calendar, which annotations cannot convey.

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 sentences, zero waste: the first states the action, the second front-loads the destructive replace caveat before the recovery instruction. No restated name or title padding.

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 3-parameter mutation with no output schema, the description covers the action, the destructive replace behavior, the recovery workflow, and the downstream effect, while the schema covers the remaining parameter semantics. It could mention the 200-item cap or error case when an invalid company id is passed, but nothing essential 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 projectId, workspaceId, and companyIds are already documented in-schema, including the replace semantics of companyIds. The description reinforces that replace semantics but adds no syntax or format detail beyond the structured fields, so the 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 and resource ("Set the brands the user follows in Sightglass") and immediately clarifies that this is a full replace, not an incremental follow. An agent can distinguish this from read-oriented siblings like sightglass_list_saved or sightglass_get_company without opening a 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?

Explicitly names the prerequisite read step and the alternative tool ("read the current one with sightglass_list_saved (kind=following) and include the ones to keep"), giving an actionable read-modify-write workflow. It also states the downstream consequence (home view and offer calendar) that motivates using it at all.

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