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

Annotations already declare readOnlyHint, idempotentHint and openWorldHint=false, so safety is covered. The description adds genuinely useful behavioral context beyond that: it is plain-language/low-authority in nature, cites CRA sources, and returns an as-of date that signals data freshness — a detail 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?

Two sentences, front-loaded with the audience and the covered facts, followed by the return shape. Dense but every clause names a distinct fact or field; slightly list-like, but no filler sentences.

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 an output schema present the description need not restate return values, yet it adds a helpful gloss on the structuredContent fields and the as-of date. The only gap is the absent sibling/differentiation guidance against gst_hst_rate_by_province and gst_hst_small_supplier_check.

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?

The tool takes zero parameters, so the baseline is 4. There is nothing to disambiguate, and the description correctly spends its words on output scope instead.

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 states a specific subject (Ontario HST basics for businesses) and enumerates the exact facts it covers — 13% rate, $30,000 threshold, 29-day registration deadline, place-of-supply rule — with CRA sourcing. It does not, however, explicitly differentiate itself from siblings like gst_hst_rate_by_province or gst_hst_small_supplier_check, which cover overlapping facts.

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?

Usage is implied by the content scope (a plain-language primer on Ontario HST), but there is no explicit when-to-use guidance, no statement of when to prefer gst_hst_rate_by_province or gst_hst_small_supplier_check, and no mention of prerequisites or limits. An agent must infer the routing decision itself.

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