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

Annotations already declare read-only, idempotent, non-destructive, closed-world behavior, and the description adds meaningful operational facts on top: free (0 credits), keyless calls work but are rate-limited per IP, values are unmodified from the BNR source, and output is informational only. This is exactly the kind of context annotations cannot 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?

One dense but well-ordered sentence: acronym expansion and unit first, then the returned values, then the history modes, then cost/auth/source caveats. Every clause carries information, though the compressed punctuation makes it slightly harder to scan than it could be.

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?

For a 4-param, zero-required, no-output-schema read tool, the description covers what is returned in each mode, the enum semantics, the cost model, keyless rate limits, and provenance. An agent has everything needed to choose a mode and call it correctly without further inference.

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 0%, so the description carries the full burden and largely does: it explains that 'date' yields the applicable quarterly value, that 'history' takes the daily or quarterly enum, and that daily history pairs with from/to. Only 'to' is left implicit as the endpoint of the from/to range rather than explicitly defined.

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 names a specific resource (the IRCC consumer-credit reference index, % p.a.) and spells out exactly what the tool returns: the quarterly value applicable on a date plus the next quarter's value if published, the latest daily value, or a history series. It is clearly distinguishable from siblings like get_robor or get_bnr_exchange_rate by resource, though it never explicitly contrasts itself with them.

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 gives concrete mode selection guidance: use 'date' for the point-in-time value, or 'history' with type daily plus from/to, or type quarterly. That is clear operational context, but there is no explicit statement of when *not* to use it or which sibling tool to pick instead.

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