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

The readOnlyHint=true annotation already tells the agent this is a safe read. The description adds the underlying endpoint (GET /contacts/{id}), which hints at passthrough semantics, but says nothing about error behavior (e.g., not-found), permissions, or what the response contains.

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?

Two short sentences, purpose first and the endpoint mapping second. Nothing is wasted and the key information is front-loaded.

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 single-parameter read tool with a readOnly annotation, the definition covers what an agent needs to invoke it. The only real gap is that no output schema exists and the description doesn't characterize the returned contact fields, though that is minor at this complexity.

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% for the single contact_id parameter, so the schema already carries the semantics. The description only restates that lookup is by id and adds no format, sourcing, or validation guidance.

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 and resource ('Get one contact by id') and the 'by id' qualifier implicitly separates it from siblings like rinkel_list_contacts and rinkel_find_contact_by_number. It stops short of naming the alternatives explicitly, so it is clear but not fully differentiated.

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 'by id' phrasing implies the precondition (you must already have a contact id), but there is no explicit statement of when to use this versus rinkel_find_contact_by_number or rinkel_list_contacts, and no mention of what happens when the id is unknown.

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