verify_email

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

Goes well beyond the annotations by disclosing the credit cost ('Spends 1 verification credit per call') and a zero-cost sandbox domain with canned fixtures for each verdict. The annotations already declare openWorldHint=true and idempotentHint=false, and the description complements rather than repeats them.

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?

Front-loaded with the verb and the verdict set, then cost, then the free-test-domain tip last. Every sentence carries information an agent needs; the return-value enumeration is justified because no output schema exists.

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?

With no output schema, the description supplies the return shape (verdict enum, 0–100 confidence, safeToSend, signals) and the cost model. For a 3-parameter read-style verification call, nothing material is missing.

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 description coverage is 100%, so email, smtpProbe and catchAllDetection are already documented with defaults. The description adds no meaning about the two boolean probes (e.g. cost or latency tradeoff of skipping SMTP), so it sits at the baseline.

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 ('Verify whether a single email address is real and safe to send to, in real time') and the word 'single' implicitly separates it from the batch sibling. An agent can distinguish it from check_mx/check_spf/verify_batch without opening 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?

The 'single email address' framing plus the test-domain tip gives clear context for when this tool applies and how to exercise it for free. It does not explicitly name exclusions (e.g. 'use verify_batch for lists'), so routing guidance is strong but not fully spelled out.

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