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

Annotations already declare readOnlyHint=true and destructiveHint=false, but the description adds substantial context beyond them: the upstream source (Inventory Ledger Summary View, aggregateByLocation:FC), the default snapshot behavior, and the crucial caveat that ledger data is account/region-level with rows surfacing tenant-wide and anchored to the primary marketplace. That marketplace scoping caveat is genuinely useful behavioral disclosure for an agent.

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?

Front-loaded with the core purpose and result shape, then routing and provenance. Dense but each sentence carries distinct information (scope, fields, alternative, source, marketplace caveat). Slightly packed, but no filler.

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?

Though an output schema exists (so return values needn't be explained), the description still covers the operationally important gaps: default snapshot date, the FC-vs-FBA routing decision, and the tenant-wide/primary-marketplace scoping caveat. Nothing an agent needs to call this correctly is missing.

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 the schema already documents all 11 parameters, establishing a baseline of 3. The description adds marginal value by echoing FC code format and snapshot defaulting, but does not add syntax or semantics beyond what the schema provides.

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 and resource ('Per-fulfillment-center on-hand inventory') and enumerates exactly what is returned: ending warehouse balance per ASIN, SKU, FC code, and disposition plus the day's signed flow components. It also names the sibling it is not (get_fba_inventory), so an agent can route 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 an explicit selection rule: 'Use this — not get_fba_inventory — when the user asks about FC-level, per-warehouse, geographic, or geo distribution of inventory.' Both the when and the alternative are stated, leaving nothing to inference.

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