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

readOnlyHint=true already establishes this is a safe read. The description adds genuine behavioral context beyond the annotation by disclosing that the tool reports live health (when each source last succeeded and whether any is currently failing), which is not derivable from the annotation or the empty 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?

Two sentences, front-loaded with the resource and its fields, then a single usage directive. No filler, no restatement of the name or title.

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 parameters, no output schema, and only a readOnly annotation, the description must define the return surface itself, and it does so completely by listing sources, weight, licence, last-success timing, and failure state. Nothing an agent needs to call this 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?

The tool takes zero parameters, so the schema has nothing to document and the description carries no parameter burden. Baseline 4 applies; the description instead spends its words on return content, which is the appropriate focus for a no-arg tool.

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 resource (price sources) and enumerates exactly what it reports: which sources are consulted, their weight, licence, last success, and current failure status. This clearly distinguishes it from get_model_price and price_history, which deal with the prices themselves rather than their provenance.

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?

"Use this to judge how much to trust a price" gives a clear condition for invocation, tying the tool to a trust/provenance decision. It stops short of naming alternatives (e.g., get_model_price) or stating when-not-to-use, so it doesn't reach a 5.

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