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

With no annotations, the description carries the full burden and does so: it discloses the ordering guarantee (registry order), the field contents, and — unusually — a deliberate omission (the eligibility rule) with the reason it is omitted (it can change without the site noticing). That is exactly the kind of behavior an agent cannot infer from an empty schema.

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?

Two sentences, front-loaded with what is returned, followed by the usage caveat. The second sentence is slightly long, but every clause (exclusion, rationale, correct behavior) earns its place.

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 cover return content, and it does: it names the fields per issuer and the ordering. It also flags the key behavioral trap (do not state the rule) that an agent would otherwise get wrong.

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 tool takes no parameters, so there is nothing for the description to disambiguate; baseline for a zero-parameter tool applies. No misleading parameter claims are made.

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?

Names a specific verb (list) and resource (issuers) and enumerates exactly what each entry carries: legal wrapper, chains, and a link to the issuer's eligibility rule. This clearly distinguishes it from siblings like list_chains and list_events, which cover different resources.

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 usage directive for the common downstream question: answer eligibility questions by routing the caller to eligibility.sourceUrl rather than stating a rule. It does not contrast with sibling listing tools, but for a zero-parameter enumeration tool that guidance is the meaningful decision point.

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