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

Annotations already declare readOnlyHint, idempotentHint, destructiveHint=false and openWorldHint, so the safety profile is covered. The description adds genuinely useful behavioral context beyond that: results are CANDIDATE links, a shared counterparty does not prove contract settlement, each link states its matching basis, and the endpoint is keyless (no auth). It does not discuss rate limits or latency, keeping it short of 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?

It is a single dense paragraph, front-loaded with the core join and scope, then the return shape and caveat. Most sentences carry distinct information, though the candidate-link caveat is restated twice ("CANDIDATE links" then "every link is labelled candidate"), which is mild redundancy.

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 carries the full burden of describing returns, and it does: payer counts and totals in UAH, tender fields (tenderID, title, buyer + buyer EDRPOU, value, status), and the per-payer candidate links. Combined with the schema's window limits and the keyless note, an agent has everything needed to call and interpret it.

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 a baseline of 3 applies. The description adds meaning on top of it by tying max_payers to a concrete behavior ("for each of the largest payers … the ProZorro tenders where that payer was the buyer") and clarifying that supplier_edrpou is both payment recipient and tenderer identity, which the schema does not spell out.

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 names a specific verb (line up / join) and two concrete resources (State Treasury receipts at spending.gov.ua and ProZorro tenders), scoped by supplier EDRPOU. This is unmistakably distinct from raw-spend siblings like ua_spend_payments or ua_spend_between, so an agent can select it without opening the 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?

It gives a clear use case ("Use for supplier due diligence across procurement and actual payments"), which tells the agent when this tool is appropriate. However, it never names an alternative sibling or states when NOT to use it (e.g., plain payment listing via ua_spend_payments), so the routing guidance stops short of explicit alternatives.

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