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

Annotations already declare this is a mutation (readOnlyHint=false) in a closed world, so the safety profile is covered. The description adds two real behavioral facts beyond the annotations: a per-unit cost of 15 credits and a token requirement. It omits whether slot purchases are reversible, whether count is capped, or what happens to an already-live campaign.

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 two compact parentheticals for cost and auth. Nothing is padded and the core action leads. The parentheticals are terse but each carries real information.

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 low-complexity two-parameter mutation tool with annotations covering safety, the description is adequate but leaves the undocumented count parameter and the return/confirmation behavior unexplained. Cost and auth are covered, which is more than most, but the gap on count is notable given the 50% schema coverage.

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 only 50%: package_name is documented in the schema, but 'count' has no description anywhere. The description does not compensate, saying nothing about what count controls, its default of 1, or any upper bound. Only the plural 'slots' loosely hints that count exists.

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 ('Add tester slots to a live campaign') with an added cost qualifier that narrows intent. An agent can distinguish it from siblings like add_app or start_campaign. It stops short of naming any sibling explicitly, so it is clear but not fully differentiated.

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 'live campaign' implies the precondition that the campaign must already be running, and '(needs a token)' signals an auth prerequisite. However, there is no explicit when-to-use versus when-not guidance and no alternatives named among the many campaign-related siblings.

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