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

Annotations already declare readOnly, idempotent, non-destructive, closed-world behavior, so the description only needs to add beyond that. It does: the auth scope (campaigns.read), the date-window bound, and the honest caveat that engagement is present only "where available" — a real data-completeness signal an agent can plan around.

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 what the tool returns, then the period constraint and the auth requirement. No filler and nothing repeated from the schema 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 an output schema present and full parameter documentation, the description only needed to cover scope, auth, and the date-window rule — all of which it does. It is slightly thin on whether large reports are paginated or truncated, which is the one remaining gap for a report-style call.

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%, so baseline is 3, but the description adds meaning the schema lacks: the 1-to-366-day window that governs the from/until pair. The remaining parameters (campaign_id, workspace_id) are already well documented in the schema and need no restatement.

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 ("Fetches the performance report for a Postly campaign") and enumerates what the report contains (planned, scheduled, published, failed content plus engagement). This distinguishes it from metadata-oriented siblings like postly_get_campaign and postly_list_campaign_posts, though no sibling is named 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?

Adds a concrete constraint for the optional period ("1 to 366 days") and a prerequisite ("Requires campaigns.read"), which helps an agent decide how to call it. However, it never says when to prefer this over postly_get_campaign or postly_get_account_analytics, and gives no exclusions.

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