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

Annotations already declare readOnlyHint and destructiveHint=false, but the description adds genuinely new facts: no credit cost and no writes, plus the non-obvious rule that output is sized for the smallest named platform. It omits that generation is non-deterministic (idempotentHint=false), so repeated calls produce different captions.

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?

A single dense sentence with the subject and source constraint front-loaded and the cost/side-effect guarantee immediately after. No clause is filler; each adds a fact the schema or annotations do not supply.

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-shape detail is unnecessary, and the description covers source, sizing, locale and destination. For a non-destructive, non-billed text generator, nothing an agent needs to invoke it correctly 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?

With 0% schema description coverage the description must carry the load, and it does: locale is explained with examples ('en, fr, …'), platforms is tied to the smallest-platform sizing rule, and generation_id/upload_id are identified as the media source. It still leaves the allowed platform values and the one-of relationship between the two IDs implicit.

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 concrete verb and resource ('Write a caption and hashtags') plus the accepted sources (generation_id or upload_id) and the sizing rule across platforms. It is specific enough to act on, though it never contrasts itself with the sibling add_captions, so an agent still has to infer that distinction.

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 clear preconditions ('already in the account') and an explicit downstream handoff ('pass the result to schedule_post'), which frames the intended workflow. It stops short of naming when-not-to-use or an alternative tool for text-only caption needs.

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