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

Annotations already declare readOnly/idempotent/non-destructive/open-world, so safety is covered. The description adds genuinely new behavioral context: the result is capped at `limit`, the underlying match set can run into the hundreds across venues and instrument types, and each row carries ISIN, venue, name, CFI and issuer LEI.

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, no filler, with the core purpose and the key ranking between the two input modes front-loaded. The final parenthetical is dense but each clause (cap, magnitude, return fields) carries distinct information.

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 correctly takes on the burden of describing the returned record shape and the total-match count. It stops short of specifying ordering of results or how the total is surfaced in the response, but nothing needed to invoke the tool 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 coverage is 100%, so baseline is 3, but the description goes further by spelling out the matching semantics — order-independent all-words-must-appear substring matching for names and exact match for LEI — and by explaining that `issuer_name` is only consulted when `issuer_lei` is absent.

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 and resource ("Search ESMA's FIRDS for every instrument reported for one issuer") and pins the search key to issuer LEI or issuer/instrument name, so the scope is unambiguous. It never names the sibling firds_lookup, so the agent must infer that this tool is the issuer-scoped variant rather than the reference/ISIN one.

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?

The description gives a clear preference rule ("by issuer LEI (exact match, preferred)" vs name fallback), which is real selection guidance between the two input modes. However, it says nothing about when to reach for this tool versus the other FIRDS or entity-resolution siblings, and there are no exclusions or prerequisites.

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