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

Annotations only declare the safety profile (readOnlyHint=false, destructiveHint=false), and the description usefully corroborates and extends it: existing copper is preserved, the 'ts' router also keeps partial copper and runs last-chance welds and plane-island bridges, and the default time budget is 120 s. It does not describe failure handling or result/job behavior, so it is good but not complete.

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 dense sentences, front-loaded with the core behavior and the sibling equivalence. Some jargon ('last-chance welds and plane-island bridges') is unexplained, but nothing is padded.

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 board-mutating routing tool with no output schema and minimal annotations, the description covers the essential preservation semantics, router mode trade-off, and time budget. It omits what happens to unrouted/open nets on failure and how the resulting job is reported, which an agent would still have to infer.

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?

With only 50% schema coverage, the description compensates meaningfully for the two enum parameters: it explains that 'ml' is the learned router service (default) and 'ts' the local router, and it supplies a default budget (120 s) for time_budget_s that the schema leaves undocumented. It says nothing about nets or pours, so it does not fully close the coverage gap.

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+resource ('keep the copper of every net it already connects and route the nets still open around it') and explicitly equates itself to a named sibling: 'route_board with preserve_existing'. An agent can distinguish it from route_board and ripup_routing without opening 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?

The 'route_board with preserve_existing' framing tells the agent when to reach for this tool versus the plain router, and it explains the router choice ('ts' local router vs the default learned service). It stops short of explicit when-not guidance or stating prerequisites (e.g. that open nets should first be diagnosed).

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