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

With no annotations provided, the description carries the full burden and does real work: it discloses the 1 CRD per-call cost, that the charge applies even to rejected calls, the 429 RATE_LIMITED exemption, and that error results carry a request_id to quote to support. That is meaningful operational context an agent cannot get from the schema. It stops short of stating auth requirements or whether results are paginated, which is why it is not a 5.

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?

Three tight sentences: purpose and filters first, cost model second, error-handling guidance last. No filler, no restatement of the tool name, and the most decision-relevant constraint (cost per call) is placed early.

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 9-parameter read tool with zero annotations and no output schema, the description supplies the two things the structured data omits: billing behavior and error/request_id handling. Return shape and pagination semantics are the remaining gap, but with a full-coverage schema and the cost disclosure present, an agent has enough to call it correctly.

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 100%, so every parameter is already documented, and the description adds only marginal meaning by glossing credit_type_id as the 'program' concept. It does not explain the relationship between referrer_email and referrer_user_id, nor how limit/offset interact for paging beyond what the schema says.

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 ('List the project's referrals') plus the three supported filter axes, so an agent immediately knows this is the read-side referral enumeration tool. It does not name the sibling tools it is distinct from (apply_referral, complete_referral, generate_referral_code), but the read-only listing framing separates it adequately.

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 implies when to use it via the filterable fields, and the cost warning implicitly discourages casual polling. However, there is no explicit guidance on when to prefer this over sibling listing tools or related referral tools, and no stated preconditions such as needing a project-scoped key.

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