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

Annotations already declare readOnlyHint, idempotentHint, and destructiveHint=false, so the safety profile is covered. The description adds the meaningful detail that PII is hashed, which tells the agent the output is sanitized. It does not disclose the default 24-hour window, the 10-destination cap, or the shape/cost of sample retrieval, all of which affect behavior.

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?

Two sentences, front-loaded with the verb and resource, with the PII note trailing as a useful qualifier. No filler, though the second sentence is terse to the point of being a fragment.

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 six parameters and no output schema, the description leaves the return shape entirely unexplained — an agent does not know whether results are grouped per destination, what 'error details' contain, or how samples are structured. For a diagnostic tool of this size that is a notable gap, though annotations and a well-documented schema cover the call mechanics.

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 83%, so parameter meaning is largely handled by the schema. The description's mention of 'optional sample events and error details' loosely maps to include_sample_events and include_sample_response but adds no syntax, defaults, or interaction detail beyond what the schema already states.

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?

States a specific verb and resource: retrieving destination delivery failures. This is distinguishable from get_destination (configuration) and get_destination_event_metrics (metrics), though the description never names those siblings explicitly.

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 — an agent can infer this is for diagnosing delivery failures — but there is no explicit when-to-use statement, no prerequisite (e.g., destination_ids must come from list_destinations, which is only noted in the schema), and no guidance on choosing it over get_destination_event_metrics or get_destination_latency_metrics.

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