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

Annotations give readOnlyHint=false, idempotentHint=false, destructiveHint=false, openWorldHint=false, but the description adds real value: it explains the algorithmic basis (offset and uncertainty from the fastest round trip), discloses the side effect that a two-station session is recorded (which is why readOnlyHint is false), and states the cost ('Costs 1 unit'). That is meaningfully more than the annotations provide.

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?

A single dense sentence with the action front-loaded, which is good, but the trailing clause 'and the stations record a two-station session carries' is awkward to the point of ambiguity about what is actually recorded. The core content earns its place; the phrasing does not.

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 one-parameter tool with a full schema and an output schema, most needs are covered: the description supplies the algorithm, the clock-domain semantics of the ping triple, the session side effect, and cost. Given annotations and schema carry the rest, little is missing beyond sibling routing.

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% and there is a single parameter, so the schema already documents the [sent_ns, remote_ns, received_ns] triple. The description restates the same semantics, adding only the parenthetical that sent/received use this station's clock and remote the other's — marginal beyond the schema. 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?

Names a specific verb+resource ('Aligns two stations' clocks') and goes on to describe the ping input and the estimated offset, making the action identifiable. However, it never distinguishes itself from any of the many pull_* siblings (pull_analyse, pull_twin, pull_replay), so an agent has no anchor for when this is the right pull tool. The final clause about the session is garbled and blurs the purpose somewhat.

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 description gives the required input shape but no when-to-use guidance, no prerequisites, and no comparison to the sibling pull_* tools that likely overlap. An agent must infer usage entirely from the mechanics. Only the implicit framing ('from repeated pings') hints at context.

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