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

Annotations declare the mutation profile (destructiveHint, non-idempotent, open-world), so the description's job is to add the details annotations can't express. It does: merge/patch semantics for omitted fields and the fact that the full updated kit is returned. It doesn't cover auth requirements or failure behavior, which is a minor gap.

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 sentences, zero padding, with the add/edit scope front-loaded and the ID/merge rules following. Every sentence carries actionable information.

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 nested-object upsert with an output schema present and a source for every parameter documented in the schema, the description is nearly complete: it explains the operation's scope, edit targeting, and merge behavior. Only error/validation behavior is unaddressed.

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% and the schema already documents every item field, the kind enum, and the media_kit_id source, so the baseline is 3. The description restates the ID-to-edit convention but adds no field-level meaning beyond the schema.

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 (add or edit) and resource (one media-kit item) and enumerates the four kinds supported. It is immediately distinguishable from siblings like media_kit_remove_item and media_kit_update_content.

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?

Explains the add-vs-edit selection rule ('Existing items use their returned ID') and the update semantics ('omitted item fields stay unchanged'). It does not name an alternative tool for bulk or kit-level edits, so it stops short of full routing guidance.

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