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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive), and the description still adds real behavior: the exact return payload and the conditional 'when a stored rule matches', which signals that a non-matching input yields no rule content. It does not describe the shape of that no-match case, but the conditional is a meaningful 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?

Three short sentences, zero filler: purpose first, return payload second, the check_invoice exclusion last. Every sentence carries distinct information and nothing is repeated.

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 adequately by naming the four returned fields. For a single-parameter read tool with strong annotations this is nearly complete; the only real omission is how it differs from get_rule.

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 the single parameter already documents both accepted forms (rule id like BR-01, or a validator message quoting one). The description restates that same duality without adding syntax, format, or matching rules, so it sits at the baseline for schema-complete tools.

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 concrete verb and resource: 'Read a stored rule named in a rule id or a validator message', and enumerates what comes back (statement, plain reading, fix, source URL). It cleanly excludes check_invoice, but never distinguishes itself from the very similar get_rule, so the sibling separation is only partial.

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?

'Does not check an invoice' is an explicit when-not that routes the agent away from check_invoice, and the accepted input forms (rule id or validator message quoting one) clarify the intended context. It stops short of exclusions or comparisons against get_rule/search_rules, which a reader would plausibly be choosing between.

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