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

Annotations already cover readOnly/idempotent/non-destructive/closed-world, so the bar is lower. The description adds real value beyond them: it discloses the return payload shape (each entry has `type` and an `example`) and the filter-vs-full-list behavior — important since no output schema exists. The '[read]' tag merely repeats readOnlyHint.

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?

Two sentences, front-loaded with the resource and its payload, then the parameter behavior. Tight overall; the leading '[read]' prefix is redundant against readOnlyHint=true and is the one wasted token.

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 no output schema and 0% schema description coverage, the description is the sole source of return-shape and parameter semantics, and it covers both. Only minor edges (invalid key handling, whether examples are literal values) are missing, which is acceptable for a simple lookup tool.

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% and the single parameter is undocumented in the schema, so the description must carry the meaning — and it does: the argument is an option key, with a concrete example (`advertisement_redirect_url`) and a clear default behavior (all options when omitted). Only the behavior for an invalid key is left unstated.

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+resource: it enumerates the keys an advertisement's `advertisement_options` map accepts, plus their `type` and `example`. That is clearly distinct from `get_advertisement` (fetches the ad itself) and from `update_advertisement_keys` (writes keys), so an agent can route without opening schemas.

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 description explains how to call it ('Pass a key ... without a key, returns every option'), which implies the discovery use case, but never states when to prefer this over `get_advertisement` or `update_advertisement_keys`, nor any prerequisite. Usage is inferable rather than declared.

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