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

Beyond the readOnlyHint/destructiveHint annotations, the description discloses the required auth scope and the exact REST path (GET /contacts/{id}), which an agent can use for debugging or permission planning. It does not cover error behavior (e.g. missing id) or whether the response is wrapped, but the safety profile is already carried by annotations.

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?

Four short, front-loaded sentences: identity, expansion, permission requirement, endpoint. Nothing redundant and nothing buried.

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?

This is a simple two-parameter read with a clear schema and no output schema; the description covers how to call it but says nothing about the shape of the returned contact beyond 'its fields', leaving an agent to discover the response blindly.

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 both parameters are already documented, including the comma-separated 'with' pattern and the 'main_address' example. The description repeats the example rather than adding new meaning, so baseline 3 applies.

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 resource and cardinality ('One contact by id, with its fields'), which clearly separates it from the list_* siblings such as smallinvoice_list_contacts. It does not say so explicitly, but the singular/plural split is unambiguous enough to act on.

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?

'Add with=main_address for the main address' and 'Needs the "contact" scope' give a prerequisite and an expansion recipe, but there is no explicit statement of when to reach for this over smallinvoice_list_contacts or sibling getters like smallinvoice_get_owner.

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