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

Annotations already declare this is a non-read-only, non-destructive, open-world operation. Beyond them, the description discloses the key behavior that null reverts the line to the automatic pick and that the change is confined to sourcing, which is real context the annotations don't convey. It doesn't detail validation or error behavior, keeping it from 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 dense sentences, front-loaded with the action and scope, with no wasted words. The null-revert and sourcing-only boundary are packed into the same compact block.

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 3-parameter mutation with full schema coverage, annotations, and no output schema, the description supplies the missing behavioral context (null semantics, sourcing scope) needed to call it correctly. Only minor gaps (validation/error outcomes) remain.

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 100%, so the baseline is 3, but the description adds genuine meaning: it identifies `refs` as the line's references and explains that `part` must come from the offer or alternatives shown in get_bom, plus the null-revert semantics. This provenance guidance goes beyond the schema text.

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 ("Pick which offer a BOM line uses") and immediately scopes the input to references plus a seller part number or MPN. It distinguishes itself from siblings by naming get_bom as the option source and framing component changes as a different operation. An agent can tell it apart from get_bom and edit_circuit without opening a 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?

Gives a clear when-to-use (choosing an offer for a BOM line), an alternative behavior (null returns to the automatic pick), and an exclusion ("Sourcing only: a different component is a circuit change"). It stops short of naming the specific sibling tool to use for a component change, but the boundary is unambiguous.

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