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

Annotations already declare readOnlyHint=true and destructiveHint=false, so the safety profile is covered. The description adds that the tool returns the rule's matching criteria and booking target, which is useful behavioral context. It does not disclose pagination, error behavior, or whether the rule is returned in an evaluation-order context beyond mentioning priority.

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 description is compact and front-loaded with the core action ('Read one transaction categorization rule by id'), followed by a useful list of returned attributes. The trailing 'Read-only.' is slightly redundant with the readOnlyHint annotation but not harmful.

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 simple read-by-id tool with an output schema, annotations, and 100% parameter coverage, the description is largely complete. It explains what the rule contains, which helps an agent know what it will get. It could mention that this is a single-rule lookup versus a list operation, but the sibling names and the word 'one' make that reasonably clear.

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 100%, so the schema already documents both parameters (ruleId and companyId) as UUID value wrappers. The description does not add meaning beyond the schema, but the baseline of 3 applies because the schema carries the full burden.

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 verb ('Read') and resource ('one transaction categorization rule by id'), and enumerates the rule's key attributes (merchants, amounts, directions, chart-of-accounts account, priority). It is clear about what the tool does, though it does not explicitly differentiate from sibling tools like transaction_get_list_categorization_rules or transaction_preview_categorization_rule.

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 description implies usage: use this when you need a single rule's details by id. It does not state when to prefer this over transaction_get_list_categorization_rules or transaction_preview_categorization_rule, nor does it mention any exclusions or prerequisites. The context is clear but no explicit alternatives are given.

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