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

Annotations already declare readOnly/idempotent/non-destructive, but the description adds genuinely new operational facts: 'Costs no credits' and a full auth requirement (OAuth host prompt or 'Authorization: Bearer acd_live_…' header with a settings URL). That auth detail is the main thing annotations cannot express, though no pagination behavior is disclosed.

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?

Front-loaded with the purpose, ordering, and cost before the call-to-action and auth block. The auth sentence is long (header prefix plus a settings URL) and could be terser, but every clause carries actionable 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?

Zero-parameter read tool with an output schema and full annotation coverage; the description still supplies cost, ordering, returned fields, auth, and next-step routing. Nothing an agent needs to call 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?

The tool takes zero parameters, so the baseline is 4. The description enumerates the fields that come back, which is helpful framing but is not parameter semantics, and with zero inputs there is nothing further to disambiguate.

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?

Specific verb+resource: 'List the competitor ads saved on the account', plus the exact ordering (newest first) and the returned fields (id, advertiser, hook, media, decode-stored flag). The 'saved on the account' scope implicitly separates it from search_competitor_ads and from get_saved_ad, so an agent can route 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?

'Start here to pick an ad to decode or place on a board' gives concrete downstream intent, pointing at decode_ad and the ad_to_canvas_card family. It lacks an explicit contrast against sibling alternatives such as search_competitor_ads (when to search instead of list), so it is clear context without exclusions.

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