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

Annotations only declare readOnlyHint and openWorldHint, so the description's disclosure of a cost ('1 spam-checker credit per successful request') is genuine added value beyond structured data. It also describes the return shape (score, risk level, per-trigger breakdown), which matters since no output schema exists. No auth or pagination detail, so not a 5.

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 sentences, front-loaded with the capability and outputs, then cost/usage, then the input constraint. No filler or repetition of the tool name; every sentence adds information.

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 two-parameter read-only tool with no output schema, the description covers purpose, outputs, cost, intended timing, and the input precondition. An agent has everything needed to decide and invoke correctly.

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 the per-parameter docs already carry baseline weight, but the description adds a real semantic constraint the schema does not enforce: at least one of subject or content must be provided (required is 0 in the schema). That constrains invocation behavior beyond what the structured fields say.

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 (Analyze) and resource (email subject/body text for spam trigger words) and names the exact outputs (0-100 score, risk level, per-trigger breakdown). This clearly separates it from siblings like verify_email or check_blacklist without needing to open any 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?

Explicitly states the use case ('Use before sending marketing/transactional email to predict deliverability') and the input precondition ('At least one of subject or content must be provided'). It lacks an explicit when-not or a named alternative sibling, so it stops short of 5.

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