Add spam blacklist entry

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

Annotations already cover safety profile (readOnlyHint=false, destructiveHint=false, idempotentHint=false, openWorldHint=true). The description adds meaningful behavior beyond that: duplicate adds fail with 409 (case-insensitive), and the ownership requirement for the domain argument. This is real value 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?

Three tightly packed sentences: purpose first, then the error condition, then the ownership constraint. Every sentence earns its place 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 mutation tool with no output schema, the description adequately covers effect, failure mode (409), and the key prerequisite. Return payload details are not described, but the critical behavior for correct invocation is present.

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 both parameters are already fully documented in the schema (including the wildcard example). The description adds only the domain-ownership constraint, which is useful but marginal against a fully documented schema. 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 (Adds) and resource (sender email/wildcard pattern to the blacklist) plus the effect scope ('always treated as spam on every domain'), which cleanly distinguishes it from add_spam_whitelist_entry and the other spam siblings. An agent knows exactly what this tool does without opening the schema.

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 clear usage context: removes ambiguity about which list is being modified and clarifies the domain-ownership prerequisite plus the account-wide scope. It does not explicitly name sibling alternatives (e.g. add_spam_whitelist_entry) or state when-not-to-use, so it stops short of a 5.

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