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

Annotations already establish readOnlyHint=true, destructiveHint=false, and openWorldHint=false, so safety needs no restating. The description instead adds genuinely useful interpretive context: what "Promotions" rolls up, that "Missing" signals a silent block that is worse than spam with a different fix, and that spamScore is in tenths with -1 as a not-scored sentinel. It stops short of stating error behavior for an invalid ID.

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 description is front-loaded with the primary result, then moves to interpretation of the non-obvious fields in short declarative clauses. Every sentence carries information an agent would otherwise have to guess, and none repeats the name or annotations.

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 no output schema, the description bears the burden of explaining return values, and it does so well: headline split, per-provider and per-mailbox breakdowns, triggered content rules, and field encoding. It is nearly complete for a single-parameter read tool; only edge-case behavior (unknown ID, unrun tests) is unaddressed.

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?

There is a single parameter with 100% schema description coverage, so the schema fully documents the ID and its source tool. The description adds no syntax, range, or format meaning beyond that, which is the expected baseline when the schema already does the work.

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 ("Returns one inbox placement run with its complete report") and enumerates the report contents, so the agent knows exactly what comes back. It does not explicitly distinguish itself from the closely named siblings list_inbox_placement_run_results or get_inbox_placement_stats_by_date, but the singular-run framing is clear enough to select it.

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 no when-to-use guidance, no prerequisites, and names no alternatives for getting the same information in aggregate or per-result form. The only hint that an ID from list_inbox_placement_runs is needed lives in the schema, not the description, so usage is left entirely to inference.

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