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

Beyond annotations, the description adds useful behavioral context: no real money moves, no region rule applies, and the same packs, sales, limits, and bonuses apply as with a card purchase. It does not explicitly state that store credit is deducted irreversibly, but the destructive annotation already signals mutation.

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 tightly written sentences front-load the core action and then add the key behavioral caveats. There is no redundant or wasted text.

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?

The tool has full schema descriptions, annotations, and an output schema, so the remaining description burden is small. The description still covers the source of store credit, equivalence to card purchases, and the no-real-money/no-region-rule caveats needed to invoke it correctly.

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 schema already explains sku, context, sale_id, sections, and snapshot in detail. The description only lightly references shop_packs' store_credit_cents and sales, adding little parameter-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?

The description states a clear verb and resource: buy a shop pack with this account's store credit. It explicitly distinguishes the store-credit purchase path from a card purchase and points to shop_packs for pack and credit data.

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?

It gives clear conditions for use: the account must have store credit, the pack/sale comes from shop_packs, and it behaves like the shop's store-credit endpoint. It implies the card-based alternative via buy_pack but does not explicitly say when to prefer that sibling instead.

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