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

Goes well beyond the annotations by disclosing credit cost, a confirmation requirement, and de-duplication behavior ('avoiding cards it already has'). The annotations only declare non-readOnly/non-idempotent/non-destructive, so this added operational context is genuinely valuable and consistent with them.

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 tight sentences that front-load the action, then cost/confirmation, then inputs, then returns. No filler and every clause carries information an agent needs.

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?

With no output schema, the description correctly compensates by stating the return values (cards added, new total, remaining credits) and covers cost, confirmation and ID sourcing. It leaves open edge behavior such as what happens when fewer than the requested new cards exist, which for a credit-spending mutation would be worth stating.

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 67%, so the description has to carry some load: it explains where deckId and platform come from via list_decks, which the bare deckId schema entry does not. The count bounds (5-30) and the enum values remain schema-only, but the mapping of each parameter to an outcome (count -> 'how many cards were added') is implied.

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?

Names a specific verb and resource ('Adds new cards to one of the user's existing NextLang decks') and adds a scope constraint ('avoiding cards it already has'). An agent can distinguish it from deck-level siblings like generate_deck or save_deck, though it never explicitly contrasts itself with add_vocabulary_items, which is the nearest neighbor.

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 precondition ('Costs 1 credit: confirm first unless the user explicitly asked') and tells the agent where to source required IDs ('Get deckId and platform from list_decks'). No when-not-to-use case or alternative tool is named, so it stops short of a 5.

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