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

Annotations already declare a safe, idempotent, closed-world read, so the baseline burden is low. The description adds useful context beyond them: it returns due dates plus the applicable threshold, and includes the official source URL and checked date, which tells the agent the output is provenance-backed.

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, zero waste: the usage trigger comes first and the return-shape summary second. Nothing repeats the title or the schema verbatim.

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?

A two-parameter read-only lookup with fully documented schema and annotations, and the description covers what comes back (dates, threshold, source URL, checked date) even though there is no output schema. An agent has everything needed to select and call it correctly.

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% and both parameters carry their own descriptions, including the self-employed note on 'type' and the calendar-year meaning of 'year'. The description restates that same individual/corporation and year framing without adding new semantics, so the schema-baseline of 3 is correct.

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 (returns) and resource (CRA instalment due dates) plus the user intents it answers, so an agent knows it is the instalment-date lookup rather than a generic deadline tool. It does not explicitly contrast itself with the sibling check_filing_deadline, leaving the filing-vs-instalment boundary to inference.

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 opening 'Call this when a Canadian user asks when income tax instalments are due or whether they have to pay instalments' gives an explicit trigger condition, and the individual/corporation split is named. There are no stated exclusions or named alternatives, so routing versus check_filing_deadline is implied rather than spelled out.

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