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

Annotations already declare readOnly, idempotent, non-destructive and closed-world, so the safety profile is covered. The description adds genuinely new behavioral context: the lookup is free and instant, and the data comes from a monthly register snapshot (staleness), plus an explicit statement of what is excluded. It stops short of auth or rate-limit detail, so a 4 rather than 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?

Two sentences, front-loaded with the return scope before the limitation and the routing instruction. Every clause earns its place: capability, data source, exclusion, and alternative tool with its argument template.

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 compensates by enumerating the returned fields and stating the data source. For a single-parameter read tool whose annotations carry the safety profile, nothing needed to call it correctly is missing.

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% and the single parameter already carries an example UEN format, so the schema does the heavy lifting. The description names the UEN but adds no syntax, format, or validation meaning beyond what the schema provides, making the baseline 3 correct.

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 (lookup) and resource (Singapore entity by UEN) and enumerates exactly what is returned: registered name, status, entity type, registration date. It also distinguishes itself from the ownership-chain path via create_audit, so an agent can separate it from its siblings without opening a 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?

Explicitly gives the when-not and the alternative: officers and shareholders are NOT in the free snapshot, and the ownership chain requires create_audit with a specific query string. It even supplies the exact argument pattern ('Ownership of <name> (<uen>)'), removing all inference.

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