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

Annotations already declare non-read-only, non-destructive, idempotent and closed-world, but the description adds granularity the annotation cannot: idempotency is scoped to (post_id, tag), and a WRITE-level account permission is required. It stops short of saying what happens when the tag name does not already exist under the account (created implicitly vs. error), which is the one behavior an agent might trip on.

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 short sentences, zero waste: action first, routing rule second, constraints last. Every sentence carries distinct information.

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?

With an output schema present and annotations covering the safety profile, the description supplies auth requirements, idempotency scope and sibling routing. Only the success/failure behavior for an unknown tag name is missing, which is a minor gap.

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?

Reported schema coverage is 0% at the top level, but the nested schema does describe tag, color enum and post_id. The description adds no parameter-level meaning of its own — notably it leaves the 'account_id must match the post's account_id' constraint and any tag-creation semantics to the schema.

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 ('Attach a tag to an existing post') and immediately contrasts with create_post, so the agent can tell it apart from the siblings that also deal with tags (create_post, remove_tag) 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?

Explicitly names the alternative path ('create_post also accepts tags=[...] at creation time') and the condition that selects this tool ('for a post that already exists'). That is a complete when/when-not rule.

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