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

Annotations already declare read-only, idempotent, non-destructive and open-world, so the safety profile is covered. The description adds real value beyond that: it discloses the mandatory API key, its upstream header, the free registration URL, and the authoritative upstream coverage — though it says nothing about rate limits or result caps.

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 routing claim and authoritative-source statement are front-loaded, and the sentence listing returned fields plus the auth sentence each carry useful information. It is a dense paragraph rather than a sculpted one, but there is no padding or repetition.

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?

With no output schema, the description usefully enumerates the return fields (identifier, title, reporting org, countries, sectors, status, dates, budget), which compensates. Auth requirements and paging are covered; what remains thin is query-construction guidance for the Solr syntax on a tool whose main axis is query, though the schema examples partly cover that.

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 (limit, query, offset, sector, country, reportingOrg, _apiKey) is already documented in the schema with examples and the Solr syntax. The description adds no parameter-level meaning, so the baseline 3 applies.

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+resource ('Searches every activity published to the IATI standard') and enumerates the publisher types and returned fields, leaving no doubt what the tool does. It distinguishes itself from web search but never names its closest siblings iati_activity and iati_transactions, so an agent must infer the split within the IATI family.

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 a clear routing rule ('PREFER OVER WEB SEARCH') plus three concrete example intents, which is explicit when-to-use guidance with a named alternative class. It stops short of exclusions (e.g. when to use iati_activity for a single record instead) and gives no guidance on narrowing an over-broad query.

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