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

Annotations already declare readOnly/idempotent/non-destructive, and the closing 'Read-only, no side effects, safe to call freely' merely restates them. What the description adds beyond annotations is genuinely valuable: the semantic trap between Squish 'Essentials' and Microsoft's legacy 'Business Essentials', and the reseller-markup rule ('never claim we're cheaper than Microsoft if msDirectAnnual < annual') that governs downstream claims.

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 imperative call directive is front-loaded, followed by a clean field-by-field breakdown, so scanning works well. It is on the long side and includes some redundancy (the read-only sentence duplicates annotations, and the 'around $5/mo' illustration could be trimmed), but essentially every block carries operational value.

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?

There is no output schema, so the description must document the return shape — and it does, field by field (label, msProductName, monthly, annual, msDirectAnnual/msDirectMonthly, selfServe) including the meaning of selfServe=false as E3/E5 sales-led. Nothing material is left for the agent to discover at call time.

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 schema carries no semantics for the description to supplement — baseline 4 applies. The description instead spends its space on return-field semantics, which is the right allocation for a no-arg tool.

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 verb and resource — 'Fetch the canonical Squish email product catalog with up-to-date pricing' — and scopes it to email tiers, which separates it from the hosting/addon/public-pricing siblings without needing to name them. An agent knows exactly what corpus of data this returns.

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 an explicit, non-negotiable trigger ('YOU MUST CALL THIS BEFORE QUOTING ANY EMAIL TIER PRICE') plus explicit exclusions ('Do not guess prices from memory', 'Do not paraphrase'). The anti-patterns it forbids are concrete, which is better routing guidance than most catalog tools get.

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