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

Beyond the read-only and idempotent annotations, it discloses that results are computed server-side from live Fortnox data and searched over all pages. It also specifies the three places searched: ledger, inbox, and attached file. Output details are left to the output schema.

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 front-loaded with the core question and then adds the key scope and data-source details. It is information-dense and mostly waste-free, though the API documentation URL is arguably extraneous.

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 two-parameter read-only lookup with an output schema and full schema coverage, the description supplies the important context: what is checked, where it is checked, when to use it, and that data is live. It could more explicitly route agents away from nearby sibling tools, but nothing needed to call it 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?

Schema description coverage is 100%, so the input schema already documents both parameters thoroughly. The description mentions invoice-number lookup and gives example numbers, but adds no syntax or format details 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 states a specific check: whether supplier invoices already exist in Fortnox by invoice number, covering the ledger, inbox, or attached files. It clearly frames the operation as a pre-upload/pre-registration existence check, which distinguishes it from sibling listing or duplicate-invoice tools.

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 gives a clear usage context: run before anything is uploaded or registered. The example question reinforces the intended scenario. It does not explicitly name alternatives or exclusions, but the when-to-use guidance is strong.

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