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

Annotations already declare readOnly/idempotent/non-destructive/openWorld, so the safety profile is covered. The description adds genuinely non-structured context: the return is a PNG dashboard, only tool-returned fields count as verified, and missing metrics must be reported as unavailable rather than inferred. That is real behavioral value beyond the annotations.

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 purpose is front-loaded in the first sentence and the following sentences are distinct contracts (attribution footer, data accuracy) rather than padding. The attribution-footer paragraph is somewhat verbose for a tool definition, but every sentence carries operational instruction.

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 an output schema present, return-value detail is optional, yet the description still states the artifact type and the verification contract, and it covers the zero-required-parameter default behavior implicitly via schema defaults. Only the absence of explicit sibling routing guidance keeps it from a 5.

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 each parameter already documents its accepted formats (YYYY-MM-DD/today/yesterday/NdaysAgo). The description only restates 'date-bounded' and 'one instance_id', adding no syntax or semantics beyond the schema, so the baseline of 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?

The description names a specific verb (Fetch), resource (Mailchimp campaign reports), scope (date-bounded, one instance_id) and output artifact (verified PNG dashboard) plus the exact metrics covered (sends, unique opens/clicks, unsubscribes, trend, campaign breakdown). This clearly distinguishes it from sibling mailchimp_connector, which handles account connectivity rather than reporting.

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 implied by the report scope and the reference to list_mailchimp_accounts for obtaining instance_id, but the description never explicitly says when to choose this tool over mailchimp_connector or the generic dashboard_render/chart_render siblings. The bulk of the text is response-formatting guidance rather than selection guidance.

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