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

Annotations already declare the tool is read-only, idempotent, non-destructive, and not open-world. The description adds useful behavioral context beyond those: the fallback role for clients without MCP resource support, and the key-dependent behavior of returning an index vs. full parameter ranges. This supplements rather than repeats structured data, with no contradiction.

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 with no filler. The first sentence front-loads the core purpose and the specific client context that warrants using the tool. The second sentence delivers the most important parameter behavior. Every word contributes to correct agent selection and invocation.

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 tool with a complete input schema and no output schema, the description covers purpose, usage context, and the key semantic nuance. It does not describe the exact response content, but for a resource-reader that is largely determined by the URI and known to the agent. With annotations covering safety and idempotence, the description is sufficiently complete for correct invocation.

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 coverage is 100%, providing parameter names and enum values. The description adds semantic value by explaining the behavioral difference when `keys` is omitted vs. provided for owlcad://schema/primitives, and notes that 'any owlcad:// URI these tools tell you to read works here' — meaning the URI parameter is not just a static enum but tied to tool-referenced resources. This is meaningful added meaning.

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 verb-resource pair: 'Reads an owlcad:// resource as a tool result.' It also clarifies the scope by noting any owlcad:// URI referenced by other tools works here, which distinguishes it from schema-only reading implied by the title. The enum in the schema reinforces the resource types without needing repetition.

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 explicitly frames when to use this tool: for clients that do not let you read MCP resources directly. It also provides conditional guidance for passing `keys` on owlcad://schema/primitives to receive full parameter ranges rather than an index. It does not name alternative tools because no sibling tool serves the same read-resource function, but the context is clear.

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