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

Annotations already declare readOnly, idempotent, open-world, non-destructive, so the safety profile is covered. The description adds genuinely useful behavior: order-independent word matching for name, exact match for LEI, and the LEI-only-if-name-absent precedence — none of which the annotations convey.

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?

Three dense sentences: purpose and matching rules first, returned fields second, sibling disambiguation last. No filler, and the information an agent needs most is front-loaded.

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 compensates by enumerating the returned fields (status, competent authority, home member state, entity type). It covers purpose, matching behavior, returns and sibling scope, leaving no material gap for calling it correctly.

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 coverage is 100%, so the schema already documents all three parameters including the name word-matching and LEI exact-match semantics. The description largely restates the schema's matching rules, adding no new syntax or format detail, so the baseline 3 is 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 (look up) and resource (a firm in ESMA's Union Register of investment firms) and scopes it as the MiFID II authorisation register. It names the exact question it answers and explicitly separates itself from the FIRDS sibling, so an agent can pick 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?

Clearly frames the question it answers ('is this entity authorised to provide investment services in the EU') and routes away from FIRDS by stating this is the firm register, not the instrument register. It stops short of naming when-not to use it beyond that single sibling distinction.

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