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

Annotations already declare idempotentHint=true and destructiveHint=false, and the description reinforces this with 'Acknowledging twice is harmless.' Beyond that it discloses non-obvious behavior: the instance verifies the counter-signature against the carried key and persists it, and the cryptographic contract (header/payload shape, SHA-256 of the receipt JWS). It does not describe failure modes or what verification rejection looks like.

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 key action and effect are front-loaded in the first clause, followed by the eligible receipt kinds and then the protocol mechanics. It is dense and packed into essentially one long sentence chain, but every clause carries information; little is wasted.

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 crypto-heavy, 7-parameter, no-output-schema tool, the description supplies the signing recipe, the verification/storage behavior, and an idempotency guarantee. Missing only error/failure handling and guidance on which credential parameter to prefer, which is a minor gap given the rich schema descriptions.

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 86%, so the 7 parameters are largely self-documenting, and the description restates the counter_signature contract rather than extending it. It adds minimal semantic detail beyond the schema (no guidance on choosing key vs. pass vs. access_token), so baseline 3 applies.

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 opens with a specific verb and resource: 'Counter-sign a receipt this item earned,' and enumerates the four kinds of receipt (promise, amended agreement, ending, refund) so the scope is unambiguous. It is not a tautology of the name/title, though it does not explicitly name a sibling tool it replaces.

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?

It gives a clear operational sequence ('Read the item to find its receipts; then send a compact JWS...') plus a prerequisite (the instance verifies it against the key you carry), and reassures that 'Acknowledging twice is harmless.' It stops short of stating when to withhold acknowledgement or naming an alternative tool.

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