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

Annotations only declare readOnlyHint=false, openWorldHint=false, destructiveHint=false. The description adds genuinely new behavioral facts: the operation is idempotent for duplicates (no error), and referenced posts and digital humans must exist; the phrase 'current account' also implies it is account-scoped. It still omits auth requirements and what is returned after a successful add.

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 action front-loaded, then type constraints, then the duplicate-behavior note. The re-enumeration of item_type values partly duplicates the schema enum, which is the only minor redundancy.

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?

This is a six-parameter mutation with a fully documented schema and no output schema. The description covers the key edge cases an agent needs to know: valid item types, existence validation, and duplicate tolerance. It could be stronger by stating where the favorite appears or how failures surface, 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 the schema already explains item_type, item_id, item_name, category, tags, and note. The description merely restates the three item_type values and mentions that category, tags, and note are optional; this adds little beyond the schema. A 3 baseline is correct.

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 verb and resource set: it adds locations, posts, or digital humans to the current account's favorites. It implicitly contrasts with remove_favorite, update_favorite, and list_favorites through the word 'add', but it doesn't name those siblings explicitly, and the scope remains clear enough to call the tool without opening the 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?

Usage is implied rather than stated: 'add to favorites' and 'duplicate favorites won't error' imply safe repeated calls, but the description never says when to prefer this tool over update_favorite or list_favorites, nor does it state prerequisites such as a logged-in account or the need to have queried the post or digital human first.

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