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

Goes beyond annotations by disclosing the internal lookup, the two failure modes with clear messages, and the no-op behavior on duplicates (reinforcing idempotentHint). It doesn't state permissions or what the success response contains, but with annotations covering safety profile this is solid added context.

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?

Three tight sentences, front-loaded with the core action and outcome, then failure modes, then idempotency. No filler.

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 simple 2-parameter mutation with no output schema and full annotation coverage, the description covers purpose, failure modes, and idempotency. Minor gap: no mention of what a successful add returns or how alert_days interacts with the tool (though the schema handles that).

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 coverage is 100%, so domain normalization (URL/www stripping) and alert_days defaults are already documented in the schema. The description adds no parameter-level detail beyond what the schema provides, 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 ('Adds a domain to the signed-in user's TLDix tracking list') plus the outcome (expiry alerts). This clearly separates it from lookup_domain (read-only lookup) and list_tracked_domains.

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?

Gives concrete conditions: it looks the domain up first, fails if unregistered or the plan limit is reached, and is a no-op if already tracked. It doesn't explicitly name sibling alternatives like lookup_domain or list_tracked_domains, but the context is clear.

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