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

Annotations already declare readOnlyHint=true, destructiveHint=false, and openWorldHint=false, so safety is covered. The description adds that this returns the account-level *library* (not campaign-attached extensions) along with internal ids, which is genuinely useful scoping context. It says nothing about pagination or result ordering beyond what the schema implies.

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 front-loaded sentence with the resource, the two supported channels, concrete example types, and the return payload. No filler or repetition of the title.

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 read-only listing tool with full schema coverage and no output schema, the description gives enough to call it correctly and to understand what comes back (library extensions plus ids). Only the practical guidance on using it as the id source for extension-attachment flows is left implicit.

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 schema already documents the name vs types filter tradeoff, paging defaults, and the channel enum. The description adds no parameter-level meaning beyond that, so the baseline of 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 (List) and resource (the account's Google Ads / Microsoft Ads library extensions), and enumerates concrete subtypes (sitelinks, callouts, snippets). It clearly separates itself from the many create_*_extension siblings, which write rather than list. It stops short of naming the distinction from related read tools like query_metadata_analytics_account.

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?

The phrase 'with their internal ids' implies the intended use — retrieving ids so they can be attached to campaigns via add_extensions_to_native_campaign — but this is inferred, not stated. There is no explicit when-to-use or when-not-to-use guidance relative to alternatives such as retrieve-style lookups.

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