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

The annotations are four uninformative false hints (readOnly=false, openWorld=false, idempotent=false, destructive=false), so the description carries the full behavioral burden. It reveals the 1-credit cost, the confirmation requirement before charging, the dedup behavior across calls, and the exact return payload (cards added, new total, remaining credits). This is rich behavioral context well beyond the annotations, with no contradiction.

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 sentences, each earning its place: core purpose + dedup, cost + confirmation gate + parameter sourcing, then return values. The most decision-relevant information (what it does, what it costs) is front-loaded, and there is zero 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?

With no output schema, the description correctly discloses return values. All three required parameters are addressable via schema plus the list_decks sourcing hint, and the absence of meaningful annotations is compensated by the cost/confirm/dedup details. The only gaps are unexplored failure modes (insufficient credits, nonexistent deck) and an explicit 'vs add_vocabulary_items' exclusion.

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% — deckId has no schema description. The description compensates for that gap with an actionable instruction ('Get deckId and platform from list_decks') that constrains both parameters' provenance and ensures the agent fetches valid values. It adds genuine meaning beyond the schema, though it adds nothing about count beyond the schema's 1-30 range.

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 specific action ('Adds new cards') on a specific resource ('one of the user's existing NextLang decks'), and adds scoping detail ('avoiding cards it already has' = dedup). This differentiates it from siblings like generate_deck (creates a deck) and add_vocabulary_items (adds vocab items), so an agent can select it without opening any 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?

The description gives clear contextual usage guidance: 'Costs 1 credit: confirm first unless the user explicitly asked' is a conditional go/no-go instruction, and 'Get deckId and platform from list_decks' names the prerequisite step. However, it never explicitly names sibling alternatives or states when not to use this tool, so it stops short of full alternative routing.

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