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

With no annotations, the description carries the full behavioral burden and does well: it discloses an external dependency (public RFC 3161 TSA), a cost of 100 units, idempotent behavior for unchanged state, and the authentication channel. It does not cover failure modes, rate limits, or the return shape, keeping it short of 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?

Four sentences, purpose front-loaded, and the cost and auth facts each carry real information. Slightly rhetorical phrasing ('the one fact here the operator cannot manufacture') adds words without adding much operational content, but overall it is tight.

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 tool with no annotations and no output schema, the description covers mechanism, external dependency, cost, idempotency, and authentication. What is missing (return format, error/permission failures) is relatively minor given the tool's straightforward single-effect action.

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 50%. The api_key parameter is already fully documented in the schema (including the 'prefer _meta' guidance), so the description's auth sentence largely duplicates it, and the required agent_id parameter has no explicit semantic explanation in either place. Marginal added value, so the baseline 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 states a specific verb and resource ('sign the agent's current state' via an RFC 3161 Time-Stamp Authority), which is concrete and not a restatement of the title. It never names or contrasts with the closest siblings (timestamp_receipt, list_anchors), so differentiation is left to inference, but the mechanism described is 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?

Usage is only implied: the cost ('Costs 100 units') and the idempotency note ('an unchanged state returns the anchor it already has') help the agent decide whether to call, but there is no explicit when/when-not guidance and no alternative tool is named. Adequate but leaves the agent to infer comparison against siblings like timestamp_receipt.

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