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

Annotations already cover readOnlyHint, idempotentHint, and destructiveHint, so the bar is lower. The description adds useful behavioral context beyond annotations: it states the empty-list behavior ('With none stored it says so') and notes that invoice_create can create a client, which helps interpret an empty result. No contradictions with annotations.

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 description is short and front-loaded with the main purpose. The final note about invoice_create is slightly tangential but still adds context about empty results; overall it earns its place without excessive verbosity.

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 list tool without an output schema, the description is complete: it names the result fields, states the empty-case behavior, and confirms no side effects. Nothing an agent needs to invoke this correctly is missing.

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 has zero parameters and the schema is an empty object with 100% coverage, so there is essentially no parameter semantics to add. The description explicitly confirms 'No arguments,' which is sufficient and aligns with the schema.

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 ('List') and resource ('every stored client') plus the exact fields returned (id, address, email, VAT id). It is immediately distinguishable from siblings such as client_add and client_delete, and even clarifies the no-argument nature of the call.

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 gives clear context for when to call this tool (need to see all stored clients) and explicitly notes it takes no arguments and writes nothing, signaling it is a safe read-only list operation. It does not explicitly enumerate when not to use it, but the purpose is self-evident among the sibling tools.

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