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

With no annotations, the description carries the behavioral disclosure burden. It usefully states that the operation is publicly readable by anyone, which is important authorization context. However, it does not mention behavior on missing serial numbers, response format, or any other edge-case behavior beyond the basic fetch operation.

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 exceptionally concise: two short sentences, with the core action front-loaded and the access note as useful supporting context. 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?

For a simple one-parameter fetch tool with no output schema, the description is largely complete. It identifies the resource, the lookup key, and the public access model. It could mention what a receipt represents or what happens when no receipt matches, but the low complexity keeps this from being a significant gap.

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 schema already fully describes the single parameter with 100% coverage. The description adds only 'by serial number,' which reinforces the parameter but does not provide extra meaning beyond 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 clearly states a specific verb ('Fetch') and resource ('a receipt'), and identifies the key parameter ('serial number'). It does not explicitly differentiate from the sibling vigil_verify_receipt, which could plausibly be confused, so it stops short of a 5.

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 supplies access context ('Public — anyone can read any receipt') but provides no guidance about when to use this tool versus alternatives like vigil_verify_receipt or vigil_journal_get. There are no explicit conditions or exclusions to guide tool selection.

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