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

With readOnly/idempotent annotations already covering safety, the description still adds real context beyond them: the data source ('from public DNS'), the response contents (score, A-F grade, spoofing-risk narrative, remediation list), the freshness of scorecards ('daily-updated'), country coverage, and non-trivial cost/access details ('$0.003 USDC per call (x402, Base mainnet)'). That price and payment-rail disclosure is exactly the kind of behavior an agent must know before invoking. It does not say what is returned for an unregistered or malformed domain, which is the main remaining gap.

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?

Two sentences, front-loaded with the primary capability and the secondary scorecard mode appended. Nearly every clause carries information (record types, output shape, cost, coverage). Minor waste in wordy phrasing such as 'says how easily fake email could be sent in the domain's name' where 'spoofing risk' would do, and the price clause sits in the same block as the capability statement.

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?

There is no output schema, and the description does the required work by describing what comes back for both modes (score/A-F grade, spoofing assessment, fixes, ranked scorecards). Cost and data provenance are stated, which matters for a paid, read-only lookup. The one unexplained case is a call with no parameters at all — since no parameters are marked required, an agent has no way to know whether that errors or returns a default scorecard.

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 meaning is already supplied; baseline is 3. The description adds only marginal semantic value — it names the subject matter of sectors ('banks, governments, regulators and telecoms') and roughly the country footprint, but it does not explain the sector/country interaction or that sector defaults to 'all'. Its 'and 6 more African countries' is also slightly out of step with the 12 codes listed in the schema.

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 first clause names a concrete verb and resource ('DMARC and SPF checker for any domain') and enumerates the record types graded, so an agent immediately knows the capability. It also distinguishes two distinct return modes (single-domain check vs. country scorecard). It does not, however, contrast itself with the plausible siblings domain_intel or za_official_domain_check, so an agent choosing between domain-lookup tools gets no routing help.

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 description clearly frames two usage contexts: 'for any domain' for the checker, and 'Also returns daily-updated email security scorecards ranking banks, governments, regulators and telecoms' for the aggregate mode. The schema descriptions reinforce the either/or ('Leave empty when checking a domain... For a ranked scorecard instead'). What is missing is any exclusion guidance — nothing says when to prefer za_official_domain_check or domain_intel over this tool.

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