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

With no annotations, the description carries the full burden and does disclose the return profile: primary/near-primary sources with cadence, access terms, and liveness ('whether the URL answered today'). That freshness signal is genuinely useful behavior an agent cannot get from the schema. It stops short of stating cost, rate limits, or what happens when no source matches.

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 'Source router' and then the return shape, so the essential facts come first. The long parenthetical domain list is functional but heavy; it could be trimmed without losing routing accuracy.

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?

No output schema exists, and the description compensates by describing what each returned source includes (cadence, access terms, liveness). Combined with a fully documented two-parameter schema, an agent has enough to call it correctly. Missing only edge-case behavior such as empty results or the limit's effect on ranking.

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 both parameters are already documented (query examples, limit default/max), which sets the baseline at 3. The long domain taxonomy in the description does extend the query parameter's semantic scope beyond the schema's three examples, but it reads as tool scope rather than parameter guidance, so no strong lift.

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 concrete verb and resource ('Source router... returns the primary or near-primary sources to read') and enumerates the covered domain extensively, so the agent knows this is a routing/lookup tool rather than a data fetcher. It does not explicitly name a sibling, and its domain list overlaps with siblings like get_stablecoin_supply and list_custody_incidents, so the reader must infer that find_source returns sources while those return values.

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 trigger: 'Use before answering a factual question so the citation is the primary source.' That is an actionable when-to-use. It offers no exclusions or alternatives (e.g., when you already hold a primary source, or when you want the datum itself rather than a pointer), which is a real gap given how much the sibling set overlaps this tool's domain.

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