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

Annotations indicate a write operation (readOnlyHint=false), and the description confirms by stating it adds a domain. It additionally reveals the return value (DNS records) and a critical temporal constraint (cannot send until verification), going well beyond the annotations.

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?

The description is two sentences, front-loading the core action and output in the first sentence, with an important qualification in the second. Every sentence adds value with no redundancy.

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, single-parameter tool with no output schema, the description fully covers what the tool does, what it returns, and the follow-up required. It is complete given the low complexity and rich structural information from the schema and annotations.

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?

The schema already provides a clear description for the single parameter ('Domain to add, e.g. example.com') with 100% coverage. The description adds no extra meaning for the parameter, meeting the baseline expectation but not exceeding it.

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 uses a specific verb ('Add') and resource ('sending domain') and clearly states the additional output ('return the DNS records to publish'). It distinguishes from sibling tools like verify_domain and check_dmarc by focusing on the initial addition step.

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 description provides explicit post-condition context ('The domain cannot send until those records are live and verify_domain succeeds'), guiding the agent to follow up with verify_domain. However, it does not explicitly contrast with alternatives or state when not to use this tool.

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