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

Annotations already declare readOnlyHint=true, so "Read-only" is redundant, but the description adds real behavioral detail: ordering (newest first), separate per-stream capping, and the goalsTruncated/clicksTruncated signals that older events exist. It stops short of covering the applicationId/auth behavior (personal keys failing with MCP_APPLICATION_REQUIRED) and the includeFlowRuns permission, both of which live only in the schema.

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 compact sentences, front-loaded with what is returned and then layering sibling routing, exclusions, and capping semantics. Every clause carries information; nothing is padded.

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?

There is no output schema, so the description carries the return-shape burden and does so: it names the event types returned, their ordering, the presence of all-time goal totals, and the truncation indicators. Combined with a fully documented input schema, an agent has what it needs to call this correctly.

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 100% and every parameter is documented there in detail, so baseline 3 applies. The description reinforces the `limit` semantics (goals and clicks capped independently, truncation flags) but adds no parameter detail the schema lacks, and it omits mention of startDate/endDate, applicationId, and includeFlowRuns entirely.

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 ("Return one contact's engagement history") with an explicit scope: goals, clicks, all-time totals, newest first. It also names the sibling it is not ("per-contact companion to get_broadcast_analytics (which is aggregate)") and excludes non-events (typed replies, commands, website visits), so it is distinguishable from neighbors without opening schemas.

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?

Gives a concrete when-to-use-vs-what: use this rather than get_broadcast_analytics when you need a single contact, and "Call list_contacts first to find the contactId" supplies the prerequisite step. The exclusion sentence ("typed replies, commands and website visits never appear") heads off a common wrong expectation.

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