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

Annotations already declare readOnlyHint, idempotentHint, destructiveHint=false and closed-world scope, so the safety profile is covered. The description adds that friction and elevation losses are both modeled, which is useful physical-behavior context, but says nothing about the underlying formula (Hazen-Williams vs Darcy), fluid assumptions, or result units.

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 tight sentences with the purpose front-loaded and no filler. The 'Returns: {equiv_length_m}' fragment is partly redundant with the existing output schema, which keeps it just short of a 5.

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 an output schema present, return values needn't be spelled out, and annotations carry the safety profile. However, a calculator with 5 physics parameters and a documented result should state its modeling assumptions and result units; the description leaves the agent to infer that this is per-segment steady-state water flow.

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 all five parameters including fittings_count and elevation_change_m are already documented with units and defaults. The description adds no further parameter meaning beyond echoing 'friction and elevation', so the baseline 3 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 states a specific verb and resource ('Calculate water pressure loss in a pipe circuit') and scopes it to 'friction and elevation', which distinguishes it from plumbing siblings like calculate_pipe_flow_rate or calculate_pipe_diameter. It stops short of naming a sibling it is not, so an agent must still infer the boundary against those tools.

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?

'See list_bundles for related plomberie calculators' is a discovery pointer, not usage guidance. It never says when to pick this tool over calculate_pipe_flow_rate, calculate_hydraulic_pressure, or calculate_pump_power, nor whether it covers a single pipe segment or a whole circuit.

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