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

Annotations already declare readOnlyHint=true and destructiveHint=false, and the description adds behavioral context: it produces a spend total and overlap count, notes that category recognition is automatic, and clarifies it is a free preview with limited features. This goes beyond the schema and annotations, though it does not describe the exact return format (numeric vs. text) or pagination, which is minor given the simple nature.

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, no fluff. The first sentence front-loads the action, input format, and key output; the second clarifies scope (free vs. paid) with a URL. Every part is purposeful and easy to parse.

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 a single parameter and no output schema, the description carries the burden of explaining both input and output. It explains the input format in detail and states the two outputs (spend total, overlap count). It also mentions the paid version's limitations, which is useful context. It does not specify the exact format of the spend total (e.g., currency, monthly vs. annual), but for a read-only, low-complexity tool, this is acceptable.

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 includes an example, so baseline is 3. The description adds meaning by explaining that common tool categories are auto-recognized, category is optional, and that the tool counts overlapping categories—information that helps the agent understand how the subscription string is parsed and what the output represents. This goes beyond the schema's syntax description.

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 states a specific verb ('Get') and resource ('spend total for a pasted list of SaaS subscriptions') along with the output ('count of categories with likely overlap'). It clearly distinguishes itself from siblings by focusing on SaaS subscription auditing, which is unique among the listed tools. No ambiguity about what the tool does.

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?

The description implies usage context by specifying input format and the free-versus-paid scope. It does not explicitly name alternatives or exclusions, but given the sibling list is entirely different domains (accessibility checks, calculators, etc.), the intended use is unmistakable. Could be improved by a short 'Use this when...' statement, but the context is sufficient.

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