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

Annotations already declare readOnlyHint=true and openWorldHint=false, so safety is covered. The description goes beyond that by disclosing what the response contains — verification status and per-domain DNS record requirements broken out by type (DKIM, SPF, MAIL FROM, return path, DMARC), which is the genuinely useful behavioral detail for this tool.

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?

One sentence, front-loaded with the verb and resource, with the returned fields enumerated in a trailing parenthetical. Nothing is redundant and nothing needs to be re-read.

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 read tool with no output schema, the description covers purpose, scope, and return content adequately, and annotations carry the safety profile. Minor gap: no indication of ordering, pagination, or behavior when the project has no domains configured.

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 single parameter has 0% schema description coverage, so the schema provides no meaning for project_id. The description partially compensates by framing the result as "the project's sending domains," implying project_id scopes the list, but it adds no format, default, or source for that ID.

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 ("List") with a specific resource ("sending domains") and adds the project scope plus the returned payload (verification status, DNS records). It distinguishes itself from get_sending_domain/check_sending_domain by the plural collection phrasing, though it never names those siblings explicitly.

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 rather than stated: you'd call this to see all domains with verification state and required DNS records. There is no explicit guidance on when to prefer this over get_sending_domain (single domain) or check_sending_domain, both of which sit adjacent in the toolset.

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