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

Annotations already establish readOnlyHint=true and openWorldHint=false, so safety is covered. The description adds genuinely non-obvious behavior: the Phase-25 engine reuse, the underlying POST /api/pdn/analyze endpoint, and that missing arguments are auto-derived from stackup, BOM passives, and power-tree rails. It does not describe result labeling or the caller-asserted consequence of omitting user_request, which is left to the 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?

Front-loaded with the analysis scope followed by invocation guidance in two compact sentences with minimal waste. Slightly dense with enumerated outputs, but every clause carries information.

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 analysis results (violations, recommended caps). It covers the zero-required-parameter invocation model and the server-side derivation of inputs, leaving only minor gaps about result labeling.

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 description coverage is 100%, so the baseline is 3. The description's statement that inputs are derived server-side overlaps with what the schema already says for each optional parameter ("Derived from ... when omitted"), adding little new per-parameter 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?

States a specific verb and resource (run PDN impedance analysis) and enumerates the concrete outputs: interplanar plane-pair capacitance, multi-cap decoupling impedance vs. target, violations, and recommended caps. This clearly separates it from sibling analysis tools like run_stackup_solver and run_thermal_analysis.

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 with no arguments once a design exists" gives a clear precondition and invocation pattern, and the note that inputs are derived server-side tells the agent when arguments are unnecessary. It stops short of naming alternatives or stating when not to use it, so it does not reach a 5.

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