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

Annotations already declare destructiveHint=true and idempotentHint=true, so the safety profile is covered. The description adds genuinely new context by specifying the merge semantics: included fields replace, omitted fields persist, and null clears. That explains exactly what gets overwritten and how, which the annotations alone do not convey. It stops short of noting auth or key-scoping requirements.

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 sentences, front-loaded with the operation type and target, with each subsequent sentence adding a distinct semantic rule. No filler or repetition.

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 destructive mutation tool, the description usefully covers merge/clear semantics, and no output schema means return values need not be explained. But with four parameters at 0% schema coverage and nested objects, the unexplained profile/profile_id parameters and the unstated key identity leave real gaps.

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?

With 0% schema description coverage, the description must carry the load, and it does explain the replace/omit/null behavior of the nested metric fields and the date field. However, the top-level 'profile' and 'profile_id' parameters, and what 'this key' refers to, are never addressed, leaving half the parameters undocumented in both schema and description.

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 states a specific verb and resource ('Save caller-supplied Snapchat numbers on this key's Eligibility Watch') and leads with 'WRITE', which implicitly contrasts with the read counterpart watch_get_status. It is clear what the tool does, though it never names a sibling explicitly, so the differentiation is inferred rather than stated.

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 'WRITE' marker and the save framing imply this is the mutation entry point for a key's eligibility watch, but there is no explicit statement of when to use it versus watch_get_status or check_eligibility, and no prerequisites or exclusions. Usage is implied, not guided.

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