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

Annotations already flag destructiveHint=true and idempotentHint=true, but the description earns credit by explaining exactly what the destruction consists of: 'A list replaces the saved list' while omitted fields are preserved. The note that the group chat name is untouched is useful boundary context. It doesn't cover failure behavior for an unknown contact_id.

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?

Short and front-loaded: identity of the tool, then the field rules. Sentences are terse and purposeful. The trailing line about the group chat name is slightly cryptic out of context, but it is one clause and not damaging.

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 4-parameter mutation with full schema coverage and no output schema, the description covers the essential mutation semantics (partial update, list replacement, unspecified fields untouched). Remaining gaps — error behavior for a missing contact and permission requirements — are modest.

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 the schema already documents contact_id, name, emails, and phone_numbers, including the replacement behavior. The description restates the replace/keep semantics rather than adding new detail such as accepted formats or limits, 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 verb and resource with scope: 'Changes one saved contact on this seat.' That distinguishes it from create_contact and search_contacts by implication (one existing contact, not a list or a new record). It doesn't explicitly name a sibling, so it stops short of a 5.

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?

Usage is implied through the partial-update semantics ('A field left out stays as it is'), which tells an agent this is the right tool for edits. But there is no explicit when-to-use or when-not guidance, and no pointer to create_contact for new records or search_contacts for finding the contact_id.

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