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

Annotations only supply readOnlyHint, so the description carries the burden and does so thoroughly: it explains that invitationStatus reads 'accepted' for opt-in/imported testers, that completion percentages are computed over label-gated visible-task sets and are not cross-comparable, that tag categories are opaque ids resolved via labels.categoryName, that unanswered custom fields are simply absent, and that location is country-only.

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?

Front-loaded with purpose and the sibling exclusion before field-level caveats, and every sentence carries non-obvious semantics. The single dense paragraph and the long compound final sentence about lastAnswerAt make it harder to scan than it needs to be.

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?

There is no output schema, so the description must document return shape, and it does — covering invitationStatus, completion denominators, tag/category structure, customFields entries and their absence semantics, location granularity, and lastAnswerAt. Nothing an agent needs to interpret the response is missing.

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?

The single productId parameter is fully described in the schema (100% coverage, including where to obtain valid IDs from listProducts), and the description adds nothing about it. With the schema doing all parameter work, the baseline of 3 applies rather than a penalty.

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?

Specific verb ('Get the list') + resource ('testers') + scope ('ALREADY ATTACHED to the current beta'), plus an enumeration of the payload (invitation status, completion stats, segmentation labels). It explicitly draws the boundary against listPendingInvitations, so an agent can separate this from the nearest sibling without opening a schema.

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?

Gives an explicit exclusion rule — invitees without an account are not returned, use listPendingInvitations instead — and points to listCustomFields when full field definitions are needed. It does not address other plausible alternatives in the sibling set (e.g. getTesterFunnelDetail, listApplicants), so routing guidance is clear but not exhaustive.

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