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

Annotations already declare this is non-read-only, non-destructive, non-idempotent and non-open-world, so safety is partly covered. The description adds a meaningful trait beyond that: 'Only the fields you pass are changed,' clarifying this is a patch/partial update rather than a full replace. It does not mention the approval_id workflow, but the schema covers that parameter.

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 tight sentences with no filler, and the value ('only the fields you pass are changed') is placed after the trigger context. The field enumeration is a little long but justified by the parameter count. Structure is front-loaded and efficient.

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?

An output schema exists, so return values need no explanation, and annotations plus full schema coverage carry the safety and parameter burden. The description covers the trigger and the partial-update behavior, which is enough for correct invocation. A minor gap is that it does not call out the approval_id human-approval path, though the schema documents it.

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 every parameter is already documented in the schema, including the omit-to-preserve and null-clears semantics for job, company, and food_preferences. The description's field list largely mirrors the schema rather than adding format or constraint detail. Baseline 3 is appropriate when the schema does the heavy lifting.

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 pairs the update action with an enumerated set of mutable fields (name, nickname, email, phone, birthday, job, company, food preferences, tags), making the resource and operation clear. It does not explicitly name sibling tools like contacts.create or contacts.merge, so differentiation is by implication rather than stated. Still, an agent can tell this is a partial record update.

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 trigger phrase 'When something about a contact changed and their record needs updating' gives a genuine when-to-use condition. However, there are no exclusions or alternatives — nothing says when to use contacts.create versus contacts.update, or that duplicate resolution belongs to contacts.merge. The usage context is implied but incomplete for a crowded sibling set.

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