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

Annotations already declare readOnlyHint=true, idempotentHint=true and destructiveHint=false, so the safety profile is covered. The description adds value by enumerating which measures are included (in-transit, returned, USPS tracking, spend), which tells the agent what the payload covers. It does not disclose the aggregation window, whether results are account-wide or per-campaign, or any cost/rate considerations — gaps that matter for an analytics read.

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 compact clause with no filler, and the metric enumeration is front-loaded. The only structural weakness is that it is a sentence fragment without a leading verb, which slightly blunts scannability.

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 no-parameter, no-output-schema analytics tool, the description should at minimum state the reporting period and aggregation scope so the agent can interpret the numbers. It names the metrics but leaves the temporal and scoping frame entirely unstated, which is a meaningful gap for a stats endpoint.

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?

The tool takes zero parameters, so the baseline is 4. The description does not falsely imply any inputs and does not claim filtering options that the empty schema would contradict.

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 identifies the resource domain (direct mail: letters and postcards) and enumerates the metrics returned (sent, delivered, in transit, returned, USPS tracking, spend), but it is a bare noun phrase with no verb and no statement that the tool retrieves/aggregates analytics. It also does nothing to distinguish itself from siblings like spur_get_campaign_stats or spur_get_outreach_report, which plausibly return overlapping performance data.

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?

There is no guidance on when to call this versus spur_get_campaign_stats, spur_get_outreach_report, or spur_get_billing_summary for spend. No prerequisites, no mention of time scope or filtering expectations, leaving the agent to infer everything from the metric list.

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