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

readOnlyHint=true already covers the safety profile, and the description adds value beyond that by naming the underlying endpoint (GET /api/v0/invoices/{id}) and disclosing the { meta, response } envelope, which matters because no output schema exists. It says nothing about auth or error behavior for a missing id.

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?

Three short sentences, zero filler, with the purpose front-loaded before the endpoint and return-shape details. Every sentence 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 two-parameter read tool this is nearly complete, and the return envelope is disclosed in the absence of an output schema. Minor gap: it does not describe the contents of meta/response or failure behavior.

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 both 'id' and 'fields' are already documented in the schema; the endpoint template confirms 'id' is a path parameter but adds no new format or constraint detail. Baseline 3 applies when the schema does the heavy lifting.

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 specific verb and resource ('Fetch a single invoice') and the scope word 'single' cleanly distinguishes it from the sibling list_invoices. An agent can tell this is a by-id retrieval without opening the schema.

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?

Usage is only implied by the 'single invoice' scoping; the description never says when to prefer this over list_invoices or accelo_request, nor what happens if the id does not exist. Adequate but with a clear routing gap.

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