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

Annotations already establish read-only, idempotent, and non-destructive behavior. The description adds valuable context that these are 'active' domains registered by attackers and intended for phishing, which goes beyond the structured fields. It does not fully describe rate limits or cache behavior, but given the annotation coverage, the additional context justifies a score above baseline.

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 description is three focused sentences: purpose, technical scope, and sibling differentiation. Every sentence carries distinct value with no filler or redundancy. It front-loads the core action and immediately clarifies boundaries.

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?

Given the tool's moderate complexity, full schema coverage, explicit annotations, and presence of an output schema, the description covers the essential context. It explains what the tool detects, why it matters (phishing), and how it differs from related tools. Additional return-value details are unnecessary because the output schema is available.

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?

The input schema has 100% description coverage, with each parameter (domain, format, force_refresh) already documented. The tool description does not add further parameter-level detail, but it also does not need to because the schema is sufficient. Baseline score of 3 is appropriate.

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 uses a specific verb ('Detect') and clearly identifies the resource: active typosquat and lookalike/homoglyph domains that impersonate a brand and could be used in phishing. It further specifies technical detail (character-substitution and visual-confusion domains) and explicitly distinguishes itself from sibling tools, making its purpose unambiguous.

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 explicitly names comparator tools and defines boundaries: 'Distinct from check_shadow_domains (TLD variants with auth gaps) and discover_brand_domains (legitimate brand portfolio).' This tells the agent when to prefer this tool over alternatives and clarifies what it does not cover.

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