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

Annotations already declare destructiveHint=true and idempotentHint=true, so the description's job is to add context — and it does: the shared photo never goes to Dashly, the output is a friendly likeness rather than a portrait, and an unnamed new animal auto-gets a default name. It does not spell out that setting a companion replaces/overwrites the existing one, which is the main remaining behavioral gap for a destructive tool.

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 dense sentences, front-loaded with what the tool changes before the mode-specific rules. All sentences carry information an agent needs (rename rule, photo handling, default naming). Slightly heavy, but nothing is redundant.

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. The description covers the two operating modes, the privacy-sensitive photo path, the naming defaults, and the spec sourcing, which together with the nested schema is enough for an agent to call this correctly.

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 67% and three params exist, so the schema does substantial work. The description still adds real semantics beyond it: 'name alone' means rename, spec must be filled from the fixed lists, and the animal kinds carry default names (Pip, Bao, Lumi). It does not clarify required-vs-optional spec fields for the person kind, but overall it compensates for the partial schema 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+resource (set/change the companion) and immediately explains what the companion is and where it surfaces (status tile, calendar, logging). The named characters and the person option make the scope concrete, and no sibling tool touches this resource, so it is trivially distinguishable from the dashboard/topic/entry tools.

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 mode-level guidance: pass a name alone to rename '(only when the person asks)', and use the photo-and-spec path when the companion is a person. It does not name an alternative tool, but no sibling overlaps this resource, so there is nothing to exclude. Clear context without explicit when-not rules.

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