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

Annotations already cover readOnly/idempotent/non-destructive, and the description adds substantial context beyond them: no action execution, wallet access, policy storage or decision history; stateless per-call rules; unauthenticated source labels; a limited phrase heuristic with false positives/negatives; and that usage metadata but not request bodies is recorded. These are exactly the caveats an agent needs before relying on an ALLOW result.

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 core behavior and return values, then routing, then limits — a sensible order. It is a dense single paragraph, though, and a couple of points (contract scope, payment activation) could be split for scanability rather than compressed into the same block.

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 an 11-parameter, nested-object tool with an output schema, the definition covers activation conditions, precedence, failure mode, trust boundaries and statelessness. Nothing an agent needs in order to call it correctly or interpret the verdict is 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?

With 100% schema coverage the baseline is 3, but the description adds cross-parameter semantics the schema states only locally: action.type=payment activates spending checks and requires amount with remaining_budget, and contract governs data rather than action. It doesn't restate the merchant/allowlist coupling, which is already in the schema, so this sits just above baseline.

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 and resource: evaluate a proposed action against evidence, source allowlists, data constraints and payment limits, returning ALLOW/BLOCK with reason codes. The enumerated inputs and the return contract make it unmistakable against the sibling validation/spend tools without opening the schema.

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?

Gives an explicit routing rule set: 'Use this gate before execution, trust_check_spend for budget alone, or trust_validate_data for structure alone', plus the operational directive to enforce BLOCK and fail closed. It also states a precedence constraint (evidence cannot override an over-budget payment), so the agent knows how the checks combine rather than just which tool to pick.

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