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

Annotations already cover readOnlyHint/destructiveHint/openWorldHint, and much of the description is output semantics rather than behavior. It still adds genuinely useful behavioral caveats beyond the annotations: charged_unmeasured_runs are "never counted as zero," credits are measured across the whole provider account, and budgets with null mean no limit. It omits auth/permission or rate-limit behavior, so not a 5.

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 clause, and every subsequent sentence carries substantive content needed by a tool with no output schema. However, the sentences are long and parenthetical-heavy (embedded metric definitions, budget caveats), which hurts readability and pushes it below a 5.

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 carries the return-value burden and largely meets it, enumerating records_sent, credits_charged, charged_unmeasured_runs, verifications_spent, last reported balance, CRM write allowance, budgets and notes. It stops short of fully specifying units (currency for credits) and the exact shape of budgets, leaving minor interpretive gaps.

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%, so the schema already documents top, since, until, group_by and connection_id; the baseline is 3. The description adds only a small amount (grouping dimension and "largest first" ordering), and never addresses top or the ISO 8601 date formats, which the schema handles.

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 opening clause states a specific verb and resource (what the connection's runs spent over a date range) plus grouping and ordering, so an agent immediately knows this is a usage/cost report. It is not confused with siblings like get_run or list_runs, but it never names a sibling or explicitly distinguishes itself from them, so it stops short of a 5.

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?

It gives a concrete when-to-use: "read it before dispatching to know your headroom," which ties the tool to a workflow decision. It also clarifies the read-only posture ("Reads only; calls no provider"). There is no when-not-to-use or named alternative, so it is clear context without exclusions.

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