estimate_impedance

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

Annotations already declare readOnly/idempotent/non-destructive, so the safety bar is low; the description adds the underlying model (IPC-2141 closed-form) and clarifies that dielectric_mm changes meaning by geometry (height-to-plane for microstrip, plane-to-plane for stripline). It does not discuss accuracy limits or tolerance vs. a field solver.

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?

Three short, front-loaded statements with no filler: what it computes, the geometry-dependent meaning of the key input, and the two alternative tools. Every sentence earns its place.

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 6-parameter computational tool with no output schema and 0% schema coverage, the description should also say what comes back (e.g. impedance in ohms) and cover gap_mm (likely differential-pair spacing). It handles the core geometry case well but leaves the return value and part of the parameter set implicit.

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 0%, so the description must carry parameter meaning. It does explain dielectric_mm per geometry and names the microstrip/stripline values for geometry, but width_mm, copper_mm, gap_mm, and er are left unexplained, so the compensation is only partial.

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 ('closed-form (IPC-2141) impedance estimate for a hypothetical trace') and explicitly scopes it as what-if rather than measurement. It also names the two overlapping siblings (get_layer_stack, check_impedance) so the agent can separate this tool from them without reading any schema.

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 routes the agent away from this tool by naming alternatives: get_layer_stack for real stack-up thicknesses/Er and check_impedance for every routed pair. The condition selecting this tool ('hypothetical trace') is implied rather than spelled out, but the sibling differentiation is clear.

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