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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive), but the description adds genuinely useful behavior: zero credit cost, the guarantee that no decode is executed, conditional decode presence ('when it has one'), and concrete auth steps including the OAuth flow and Authorization: Bearer acd_live_… header. It does not describe error/empty-decode handling, keeping it out of 5 territory.

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-loads the purpose, then cost guarantee, then auth requirements. Every clause earns its place, though the auth sentence is fairly long and could be tightened; still well-structured overall.

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, return-value explanation is unnecessary, and the description still covers cost, decode behavior, authentication, and the ID source. Nothing an agent needs to call this 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?

Schema description coverage is 100% and the single ad_id parameter is already documented with its provenance (from list_saved_ads or save_competitor_ad). The description adds no additional meaning about the parameter, so the baseline 3 applies.

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 (read) and resource (one saved competitor ad) and clarifies the scope: a single ad in full, including its stored decode when present. This clearly separates it from list_saved_ads (plural listing) and decode_ad (which would generate a decode rather than read a stored one).

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 context: it costs no credits and never runs a decode, implicitly routing decode-generation needs to decode_ad. The schema also points to list_saved_ads/save_competitor_ad as ID sources. It stops short of an explicit 'use this instead of X when Y' statement, so it is a strong 4 rather than a 5.

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