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

readOnlyHint=true already establishes the safe-read profile, so the bar is lower. The description adds only the underlying REST endpoint ('GET /invoices'), which is mild context and does not disclose pagination behavior, default limits, or auth needs beyond what the schema covers.

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, purpose front-loaded, no filler. The trailing REST-endpoint reference is somewhat redundant but compact enough not to hurt readability.

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?

A simple read-only list tool with fully documented params and annotations covering safety; an output schema is not needed for a list operation. The description is adequate, though it could note pagination defaults or the subscription-invoice distinction more concretely.

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 fully documents all five parameters. The description's mention of 'filtering, sorting, and expansion' loosely maps to where/sort/expand but adds no syntax or format detail beyond the schema, so the baseline 3 applies.

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 clear verb+resource ('List invoices') and adds the qualifier that these are typically subscription invoices, which helps position it against the swell_list_subscriptions sibling. It stops short of explicitly contrasting with that or any other sibling, so it is clear but not fully differentiated.

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 only implies usage through capability words ('filtering, sorting, and expansion'). It gives no when-to-use condition, no when-not-to-use, and does not route the agent to swell_list_subscriptions, swell_query, or the get_* siblings.

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