check_domain

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

With no annotations and no output schema, the description carries the full burden and does reasonably well: it flags the tool as paid and names the returned fields (dns, tls_valid, cert_expiry). It omits failure behavior, error semantics when tls_valid is false, and rate/timeout limits, which keeps it short of 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 short sentences: purpose, cost, returns. Purpose is front-loaded and every sentence earns its place with zero filler.

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 one-parameter read tool with no annotations, the description supplies the two things structured data lacks: cost ('Paid') and the shape of the result (dns, tls_valid, cert_expiry). Only failure/error behavior and any rate constraints are 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?

One parameter with 100% schema description coverage, so the schema already documents 'domain' with an example. The description adds nothing on format (e.g., whether a scheme or subdomain is expected), so the 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 (check) and resource (domain) and enumerates the three things verified: live DNS A records, valid TLS/SSL, and certificate expiry. This implicitly separates it from is_site_up (HTTP availability), but no sibling is named explicitly, so the differentiation is left to inference.

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 by the scope stated ('check any domain'), and 'Paid' gives useful cost context before invoking. However, it never says when to prefer this over the overlapping is_site_up sibling, nor are there exclusions or prerequisites.

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