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

Annotations already declare readOnlyHint=true, so safety is covered; the description adds the cost trait ('Free') and the content domains the call returns (layers, stings, defaults, limits, prices), which is context beyond the annotation. It does not describe output format or freshness, so not a 5.

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 short sentences, front-loaded with the cost signal, then the scope. Every clause earns its place and nothing is redundant with the schema.

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 zero-parameter read tool with no output schema, the description should say what comes back, and it lists the content domains. Adequate; only the return shape/nesting is unspecified.

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 and the schema has full coverage, so there is nothing for the description to disambiguate. Baseline 4 applies.

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 gives a specific verb ('Describe') and names the resource ('Delta Signal') and enumerates the content returned: layers, stings, defaults, limits and prices. That distinguishes it clearly from the siblings (audio decoding, card previewing, signature rendering/verification). It stops short of 5 only because 'Delta Signal' and 'stings' are domain jargon an outsider agent may not decode.

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?

'Free' signals there is no cost barrier, implying it is a safe discovery call, and none of the siblings offer an overlapping capability. But there is no explicit when-to-use, no stated prerequisite for the other engine-related calls, and no exclusion of any alternative.

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