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

Annotations already cover the safety profile (readOnlyHint=true, destructiveHint=false), so the description's added value is its disclosure that the check is 'structural' only — important since it prevents an agent from treating a pass as authoritative verification. It also lists the returned artifacts (normalized formatting, masked number, last four digits) and states the 10-credit cost, which is behavior an agent cannot get from 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?

The content is dense and front-loaded: purpose first, then accepted input forms, then return values and cost. The only waste is the redundant 'Tax ID Validator: Tax ID Validator checks…' self-restatement of the title, which occupies the opening clause without adding 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 single-parameter read-only validator with an output schema, the description covers scope, accepted input forms, return artifacts, and cost — enough for correct invocation. The one remaining gap is that it explains return values the output schema already defines instead of stating what constitutes a failure or how the masks are formatted.

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?

With one parameter and 100% schema description coverage, the schema already documents that 'taxid' is an SSN/EIN/ITIN string and even supplies a formatted example. The description adds one genuine detail beyond the schema — that formatted or unformatted strings are both accepted — which is useful but marginal, so it sits at the baseline rather than above it.

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 description gives a specific verb and resource — it 'checks US tax identification numbers including SSNs, EINs, and ITINs for structural validity' — which is far more precise than the title. It does not name or differentiate against any sibling tool (e.g., CardValidator, IBANValidator, PhoneNumberValidator), but no sibling covers tax IDs, so ambiguity remains low.

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 rather than stated: the agent can infer this is the tool for validating SSN/EIN/ITIN input strings, and the response shape hints at both validation and masking use cases. There is no explicit when-to-use/when-not guidance, no mention of alternatives for other identifier types, and no note on what to do when validation fails.

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