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

Annotations already cover read-only, idempotent, open-world and non-destructive behavior, and the description adds genuinely new context: the empty-filter clarification behavior, the shape of the return (lender's own rate wording, conditions, check date, source link, accompanying notice), and a non-advisory disclaimer. It adds no detail on result volume or how the max limit of 10 interacts with paging, so not a 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?

The opening sentence is long and semicolon-chained, but every clause carries load-bearing information: filters, no-filter behavior, return contents and scope limits. Nothing is redundant, though the run-on construction makes it slightly harder to scan than a shorter front-loaded statement.

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 nine optional parameters, no output schema and annotations covering the safety profile, the description does the important work: it explains the empty-input path, summarizes the return payload, and prevents off-label use. The remaining gap is that fees and sort are left unexplained anywhere, so an agent must guess what ordering and fee-filter values do.

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 only 56%, and the description names six of the nine filters (mortgageType, term, position, minimumLtv, purpose, lender keyword) but never mentions fees, sort or limit, which have no schema descriptions at all. The facts it does add, such as keyword meaning a lender or directory term rather than a person, largely restate what the schema already says for those fields.

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?

The description gives a specific verb and resource ('searches the Ontario mortgage rates lenders have published') plus the data source (Open Mortgage Rates) and the concrete filter dimensions available. It also bounds scope negatively ('takes filters only, not names, contact details or dollar amounts'), which cleanly separates it from sibling tools like analyze_mortgage_scenario or get_financing_options.

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 states the triggering user question ('useful when someone asks what rates lenders are publishing') and explains the no-filter fallback (it asks what to search for instead of dumping all records). It also rules out misuse as a quote or eligibility tool. It never names a sibling tool as an alternative, so it falls short of a 5.

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