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

Annotations already declare readOnlyHint=true, destructiveHint=false and openWorldHint=false, so safety is covered. The description adds nothing beyond that: it does not say what happens when no match exists, whether multiple contacts can match a phone or email, or which record is returned.

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?

A single front-loaded sentence with no redundant wording; the only slightly empty token is the adjective "Fast". It is appropriately sized for a simple read tool but leaves room for one clarifying sentence.

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 three parameters, zero required parameters, and no output schema, the description should tell the agent that at least one of email/phone must be supplied and roughly what a successful lookup yields. Neither is covered, leaving a real risk of an empty call or of misunderstanding the result shape.

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 all three parameters (email, phone, purpose) are already documented with formats such as E.164. The description only restates that lookup happens by phone or email, adding no meaning beyond the schema, so the 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 verb (lookup) and resource (SautiDesk contact) plus the two identifying keys, which lets an agent distinguish it from desk_list_contacts and desk_create_contact. It stops short of an explicit contrast with the nearest sibling, desk_list_contacts, so it is clear but not fully differentiating.

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 word "lookup" by a specific identifier implies the use case is resolving one known contact rather than browsing a list, which is an implicit routing hint toward desk_list_contacts as the alternative. No explicit when-to-use or when-not-to-use statement, and no prerequisites (auth, contact existence) are given.

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