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

With no annotations provided, the description carries the full burden and does well: it discloses the side effect that an unknown fieldName creates a new company-wide field, that showInTable is a per-field company-wide setting affecting the inventory table for every item, and that the saved field is returned. It omits permission requirements and what happens to an existing value on overwrite.

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?

The description is front-loaded with the core action and result, then layers the field-reuse rule and the showInTable scope note. Four tight sentences, no filler, though the showInTable explanation is slightly longer than strictly necessary.

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 four-parameter mutation tool with no annotations, no output schema, and zero schema coverage, the description covers input meaning, side effects, and the return value adequately. The notable remaining gap is the lack of differentiation from set_inventory_item_custom_field_by_name, which an agent choosing between the two would need.

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 0%, so the description must compensate, and it does: it explains the meaning of inventoryItemId, fieldName (reuse existing vs create new), value, and showInTable including its company-wide scope and default behavior. Only the expected string format of 'value' is left unstated.

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 opens with a specific verb and resource ('Sets (creates or updates) a custom field value on an inventory item') and makes the upsert semantics explicit. It does not, however, distinguish itself from the very similar sibling set_inventory_item_custom_field_by_name, so an agent cannot tell the two apart from the text alone.

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?

Usage is implied by the parameter narrative ('Provide the inventory item id, the field name...'), and the reuse-vs-create rule for fieldName is spelled out. There is no explicit guidance on when to use this versus get_inventory_item_custom_fields, list_custom_fields, remove_inventory_item_custom_field, or the by_name sibling, and no stated prerequisites.

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