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

Annotations already establish readOnly/idempotent/openWorld and non-destructive, so the safety profile is covered. The description goes beyond that by disclosing the returned fields (year-end, publication date, auditor, opinion, report links) and the coverage boundary (back to the 2000s; ESEF only from FY2020), which is genuinely useful behavioral context.

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-loads the core action and scope before the detail, and every clause (return fields, identifier options, year range, ESEF cutoff) carries information. It is dense but not padded, though slightly long for a single listing tool.

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 reasonably carries the burden by enumerating the returned fields and the depth of historical/ESEF coverage. It is nearly complete for a listing tool, with only minor omissions such as pagination or ordering behavior.

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 four parameters are already documented, giving a baseline of 3. The description adds meaning by clarifying that nif, isin and company are interchangeable issuer-identification routes, which helps the agent choose one when multiple are available.

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 (List) plus a precisely scoped resource (a Spanish issuer's annual financial reports from the CNMV register), and enumerates what each entry carries. An agent can distinguish this from cnmv_search_filings (general filings) and cnmv_find_issuer (issuer lookup) without opening any 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?

It tells the agent how to identify the issuer (nif, isin or company name) and how far back coverage goes, which aids invocation context. But it never names an alternative sibling or states when NOT to use this tool versus cnmv_search_filings or cnmv_find_issuer, leaving routing to inference.

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