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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive, not open-world), so the bar is lower, yet the description adds real value: 'opens nothing by itself' tells the agent this tool has no side effects and only returns instructions. The note that Invoice Simple publishes no public API explains why browser automation is the required path, which is context the annotations cannot convey.

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?

Purpose is front-loaded, but the phrasing is convoluted ('Returns how to do it in Invoice Simple step by step ... and opens nothing by itself') and the trailing API/plans sentence is long and only loosely tied to calling the tool. The content is mostly justified but could be tightened.

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?

For a zero-parameter, read-only tool with no output schema, the description covers what it returns at a high level (screens, buttons, fields), confirms it performs no action itself, and explains the API situation. Only a slightly more precise statement of the return format would make it fully complete.

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, so the baseline is 4; the empty schema is consistent with a parameterless listing/guide call and no parameter semantics are needed.

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 gives a specific verb and resource ('List unpaid invoices') plus an explicit scope ('the user's own Invoice Simple account'), and clarifies the otherwise misleading name by stating it returns step-by-step instructions rather than the invoices themselves. It does not explicitly name the sibling invoice tools it differs from (e.g., invoice_simple_mark_invoice_paid), but the 'unpaid' filter and guide-only nature make it distinguishable.

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 states the use case (listing unpaid invoices from an AI agent) and the follow-on action ('then do it with the cotlet_browser_* tools in the user's Invoice Simple Cloud Browser'), which is genuinely helpful routing. However, it never says when not to use it or contrasts it with the other invoice_simple_* siblings, so the guidance is implied rather than explicit.

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