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

Annotations cover the safety profile (read-only, idempotent, closed-world), and the description goes well beyond them: it names the data sources (CMHC RMS, Bank of Canada), lists the calculation assumptions (20% down, 25-year amortization, ~1%/yr taxes, $150/mo heating), and explains the two distinct output readings. This is rich behavioral disclosure.

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-loaded with the usage trigger, then data sources, assumptions, return shape, and limitation in dense but non-redundant sentences. Every sentence 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 carries the return-value burden and does so by describing the two readings (cash outlay vs. economic cost) and the coverage limitation. Nothing an agent needs to call or interpret the tool 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% with a single required "ville" parameter, so the schema already documents the input. The description adds nothing syntactic about the parameter, which is the correct baseline when the schema does the work.

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 decision-support purpose (rent vs. buy in a Canadian city) with the exact quantities compared — CMHC two-bedroom rent vs. carrying cost of the reference home. This clearly distinguishes it from data-only siblings like taux_courants and stats_marche.

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?

"Call this when the user wonders whether to rent or buy in a Canadian city" gives explicit triggering context, and the trailing note about CMHC-covered metros implies when the tool will not apply. It stops short of naming a sibling alternative for related questions.

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