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

Annotations already flag this as a non-read-only, non-idempotent, open-world mutation, so the description's main added value is the two-phase confirm=false preview / confirm=true apply behavior and the fact that it writes to the account library and then attaches in one call. It does not mention rate limits or auth scopes, so it lands above baseline but not maximal.

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?

Purpose first, then compact format specs for sitelinks and callouts, then the confirm semantics in one trailing clause. No filler sentences; every clause carries information an agent needs to format the call correctly.

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?

For a 6-param mutation with an output schema present, the definition covers the semantics of the two content params, the confirm flag, and the attach behavior. The missing bits are the untouched identifier params (campaign_id/account_id/customer_id) and any note on error/partial-attach behavior, which are real but modest gaps.

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 0%, so the description must carry the meaning of every parameter, and it does document sitelinks format ('Display text|https://url' or 4-pipe variant, <=25 chars), callouts ('Free shipping'), and confirm (preview vs apply). It leaves account_id, campaign_id, and especially customer_id (which is optional and undocumented) without explanation, so it is not fully compensating.

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 (adds) plus resource (SITELINK/CALLOUT ad extensions) on a Microsoft (Bing) campaign, with a plain-language gloss of what a sitelink and a callout are. Clearly distinguishable from siblings like list_microsoft_ad_extensions and remove_microsoft_ad_extensions.

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?

Defines what each extension type is and gives format examples, and distinguishes this add-tool from the remove/list siblings by implication. It does not explicitly state when NOT to use it or explain the preview-vs-apply tradeoff beyond the confirm flag, so it falls just short of a full routing rule.

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