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

With no annotations, the description carries full behavioral burden. It discloses 'FREE' status, 'fair-use limits,' and 'per-call x402 / prepaid credits' for agents/production, which are critical constraints. It implies read-only via 'Discovery' and 'list,' though it doesn't explicitly state no modifications occur. This adds meaningful value beyond a bare list.

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 two sentences, front-loaded with the core purpose ('FREE. Discovery: ...') and efficiently communicates contents, usage, and pricing. Every sentence earns its place with no filler or repetition.

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?

Despite no output schema, the description enumerates return fields (id, name, bed/build volume mm, nozzle), lists all 12 materials with variants, and explains the pricing model. It also provides usage guidance ('pick a printer and material id'), making it self-sufficient for an initial discovery tool. The sibling context suggests a rich ecosystem, and this description positions the tool appropriately.

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 input schema is empty (0 parameters), so there are no parameter semantics to clarify. However, the description explains that the output provides `printer` and `material` ids for use in subsequent calls, giving meaning to the return values. This exceeds the baseline for 0 parameters.

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 'List 3D printers, materials and pricing' with specific details (12-printer FDM fleet, 12 filament materials), making the purpose explicit. The term 'Discovery' and phrase 'Call this FIRST' distinguish it from sibling tools like compare_printers and recommend_material, which are specialized. It uses a specific verb+resource structure.

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 explicitly says 'Call this FIRST to pick a printer and material id,' establishing clear when-to-use guidance. It also differentiates free personal/interactive use from paid agent/production use, guiding cost-conscious usage. While alternatives aren't named, its role as the initial discovery step is unambiguous.

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