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

Annotations already declare readOnlyHint=false, idempotentHint=false, destructiveHint=false and openWorldHint=true, so the safety profile is covered. The description adds that the return is a count of assets added, but says nothing about what happens with duplicate assets, partial failures, or whether previously attached assets are affected — notable for a non-idempotent mutation.

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?

The purpose is front-loaded in one line, followed by a usage line and a compact Args/Returns block; every section maps to something the agent needs. The Returns block is partly redundant given an output schema exists, costing a little space.

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 3-parameter mutation with an output schema and full annotation coverage, the description supplies the missing parameter semantics and the usage context. Remaining gaps are error/partial-success behavior and whether referenced assets must already exist, which an agent would likely need.

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 coverage is 0%, so the description carries the full burden and mostly does: it specifies customer_id must be numbers only with no hyphens, names the asset group resource name, and enumerates the per-asset fields including the nine allowed field_type values. It does not reconcile this with the schema, which types assets loosely as free-form string maps, leaving the exact item shape slightly ambiguous.

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 and resource ("Adds assets to an existing asset group") and the second sentence clarifies the lifecycle position — after creation — which separates it from create_asset_group. It does not explicitly name the close siblings link_asset_to_campaign or link_assets_to_customer, so an agent must still infer the 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?

"Use this to add more assets to an asset group after it's been created" gives a clear usage condition and implicitly excludes the create path. There are no explicit when-not conditions (e.g., when to use link_asset_to_ad_group instead) or stated prerequisites such as the asset already existing.

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