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

With no annotations, the description carries the full burden and does disclose the commercially relevant behavior: personal/interactive use is FREE under fair-use limits, while agent, production and high-volume calls incur x402 or prepaid credits. That is genuine auth/payment context an agent needs before calling. It does not describe response format or whether the fleet list is live/cached beyond the word "live".

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?

Front-loaded with "FREE." and "Discovery:", then the resource inventory, then the routing instruction, then the pricing caveat. Efficient overall, though "FREE" is asserted twice (opening token and the personal-use clause), which is mild redundancy.

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?

With no output schema, the description compensates by enumerating the fields returned (id, name, bed/build volume mm, nozzle) and the material set, so an agent knows what it will get. Missing only minor details such as pagination or the exact pricing figures, which the pricing model reference implies are returned rather than summarized.

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 takes zero parameters, so the baseline is 4. The description still adds value by explaining that the returned printer and material ids are the inputs other tools consume, which frames the parameterless call's role in the workflow.

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 (list/discover) and enumerates the exact resources returned: FDM printer fleet with id, name, bed volume and nozzle, 12 filament materials by name, and the pricing model. This clearly distinguishes it from siblings like compare_printers and recommend_material, which operate on the ids this tool surfaces.

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?

"Call this FIRST to pick a `printer` and `material` id" gives explicit sequencing relative to the other 13 tools, and the free-vs-paid split tells the agent when cost applies. It stops short of naming a specific alternative or a when-not-to-use condition, so it is strong context rather than a full routing rule.

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