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

With no annotations, the description carries the transparency burden and discloses important behavioral details: the platform fee (10%), the need to call request_platform_demand after listing, and the strategic distinction between agent-directed and legacy ad units. It does not mention reversibility, required permissions, or the shape of the response, but it provides more behavioral context than a typical minimal description.

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 description is front-loaded with '[Sell] Create an ad placement' and each subsequent sentence contributes useful detail (unit types, audience guidance, fee, follow-up). It is somewhat dense with parenthetical expansions, but still readable and earns its length.

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?

The tool has 7 parameters, no annotations, and no output schema, and the description covers core aspects: purpose, required fields, fee, and next step. Gaps remain around the return value (only placementId is implied), authentication/authorization prerequisites, and how errors or duplicates are handled, so it is not fully complete.

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 71%, and the description adds meaningful semantics for adUnitType by explaining that agent-directed units 'sell the agent's own context/decision path, not a human click' and that legacy units are for 'human-adjacent funnels.' It reinforces the description parameter ('Describe audience + surface') but adds nothing for the undocumented 'kind' and 'title' parameters.

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?

The description clearly states 'Create an ad placement (inventory slot)' with a specific verb and resource, and the '[Sell]' prefix clarifies that 'list' means listing for sale rather than enumerating. However, the name 'list_placement' is ambiguous next to siblings like 'search_placements' and 'list_campaigns', and the description does not explicitly differentiate it from those tools.

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?

It gives clear in-tool guidance: 'Prefer agent-directed units' vs 'Legacy cpm/cpc/cpa/cpl/cpi remain for human-adjacent funnels,' and instructs to 'Describe audience + surface.' It also directs the follow-up action 'call request_platform_demand(placementId) to fund first fill.' However, it does not explicitly state when not to use this tool or mention alternatives like 'use search_placements to view existing placements.'

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