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

No annotations are provided, so the description carries the entire behavioral burden. It says nothing about whether this is scoped to a workspace, how many months are returned, whether the current month is partial, or how timezone/period boundaries are handled for a read aggregation with zero annotation coverage. Only the fact that it is a breakdown is conveyed.

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?

A single front-loaded sentence with no filler or repetition. The aggregation grain and scope come first, and every word earns its place.

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 annotations, no parameters, and no output schema, the description is the only source of information about this tool, yet it does not describe the shape of the result (per-category rows vs totals, time window covered, ordering). For a zero-schema reporting tool the description should do considerably more.

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?

The tool takes zero parameters, which is the baseline-4 case; there are no arguments whose semantics need explaining. The description adds nothing here, but nothing is missing either.

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 resource (credit spend), a specific aggregation (calendar-month), and a scope (across all categories), which distinguishes it in spirit from siblings like get_credit_usage_by_agent and get_credit_usage_by_type. However, it never names those siblings, so the agent must infer the distinction from the phrase 'across all categories' rather than being told 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: 'across all categories' suggests this is the unfiltered/aggregate view versus the per-agent and per-type siblings, but the description states no when-to-use condition, no exclusions, and names no alternative. An agent gets a reasonable hint but nothing explicit to route on.

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