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

Annotations already declare readOnlyHint=true, so safety is covered. The description adds real behavioral context absent from the schema: that the schema's 0-required-param shape still demands one of two key combinations, and that reference wins over email when both are present.

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?

Front-loaded with the lookup semantics and the key-combination rule in two tight sentences; the trailing 'Virtuous: GET /api/Contact/Find' is mildly useful API mapping but not strictly needed for invocation.

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 read-only 3-parameter lookup with no output schema, the description covers the key selection logic fully. It does not describe the returned contact shape or the not-found behavior, which matters somewhat given no output schema exists.

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%, so the baseline is 3, but the description adds meaning the schema cannot: the either/or requirement between email and the reference pair, plus the precedence rule when both are supplied. It also illustrates reference_source with concrete providers.

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 (look up) and resource (a single contact) and names the two lookup keys (email vs. reference source + id). The word 'single' distinguishes it from the sibling list/search tools, so an agent can route without opening the schema.

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?

Gives an explicit invocation rule: supply either email or both reference_source and reference_id, and a tie-break ('Virtuous prioritises the reference'). It does not compare against virtuous_get_contact or virtuous_search_contacts, so the when-to-use-vs-alternative guidance is missing.

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