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

There are no annotations, so the description carries the full burden, and it discloses a lot about the behavior: the verification methods used, the three-valued outcome, that findings include time and method, and that stamps are published in a public log. The public-log exposure is an important side effect to disclose, and it does so. It omits operational traits such as permissions, latency/cost, or failure modes, which keeps it from a 5.

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?

Three sentences, front-loaded with the 'Use when' trigger, then the mechanism, then the output. Every sentence carries information and none is redundant. It is dense but not bloated.

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 7 parameters, nested objects, and no output schema, the description does the necessary work of describing the return value (a signed stamp with pass/fail/inconclusive plus findings, time, and method). It also flags the public-log side effect that the private parameter mitigates. Minor gaps remain around error conditions and the exact independence rule mechanics, but an agent has enough to call it correctly.

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 already 86% and each property explains itself, so the schema baseline of 3 applies. The description adds useful framing by connecting the checkable artifact types to the verification actions (arithmetic re-computation, quoting and value lookup, link opening, code parsing) that map onto kind, claims, sources, and language. It says nothing specific about producer or the independence rule's mechanics beyond naming 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 states a specific verb and resource: an independent, signed check of a piece of work (report, calculation, summary, filing draft, code) that returns a pass/fail/inconclusive stamp. The scope of the check (re-computing arithmetic, verifying quotes and values against cited sources, opening links, parsing code) further pins it down. It never explicitly names the siblings countersign_log and countersign_verify, so an agent gets no direct disambiguation between the three.

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?

'Use when you need an independent, signed check of work you or another agent produced ... before relying on it or handing it on' is an explicit trigger condition. The exclusion 'It never checks work it produced' sets a clear boundary on applicability, which is effectively a when-not rule. However, it gives no guidance on when to prefer this over countersign_log or countersign_verify.

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