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

Annotations already cover safety (readOnly, idempotent, non-destructive, closed-world). The description adds genuinely new behavioral context: it discloses the return shape ('Returns ok with the error list') despite no output schema existing, and draws the shape-vs-record boundary. It does not mention auth or any limits, but for a pure validator this is more than adequate.

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 resource, then a colon-delimited checklist and a closing scope statement. Two sentences, no filler, and the constraint clause is placed last where it reads as a qualifier. The checklist is dense but every item is a distinct validation rule.

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 compensates by stating the return value ('ok with the error list'). The single required parameter is fully documented and the tool's read-only nature is covered by annotations. Complete enough for an agent to call it correctly; only the absence of a named alternative keeps it from the top score.

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% with a single 'document' parameter, so the schema already carries the parameter meaning; the baseline for high coverage is 3. The description's enumeration of expected document properties is useful but describes validation rules rather than adding syntax or format meaning to the parameter itself.

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/Validate') and resource ('one ecca.claim-protocol 1.0 document') and enumerates exactly what is checked (versioned, engine slots, cause split, consent, seal). The scope-limiting clause 'validates shape, never the record behind it' implicitly separates it from siblings like ecca_verify, but no sibling is named, so differentiation is inferred rather than explicit.

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 closing clause 'validates shape, never the record behind it' functions as an explicit when-not boundary, telling the agent this is not the tool for validating the underlying record. It stops short of naming the alternative tool to use in that case, so it is clear context without full routing.

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