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Backpack Battles MCP

Backpack Battles MCP

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bpb_sell_item

Sells an item in your backpack for immediate gold; move storage-box items back to the backpack with bpb_place_item before selling.

Instructions

出售背包里的物品，立即获得金币（价格见 state.backpack.items[].sell_price）。储物箱里的物品需先 bpb_place_item 放回背包再出售。

Tool call template

Replace each placeholder with a value matching the input schema. Only required parameters are included; add optional parameters as needed.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {
      "item_id": "<item_id>"
    },
    "name": "bpb_sell_item"
  }
}

Input Schema

NameRequiredDescriptionDefault
item_idYes背包内物品 id

Schema Changelog

Changes observed during successful MCP inspections.

  1. First observedv0.1.0

TDQS

A4/5.0
Behavior3/5

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

With no annotations, the description carries the full burden. It does disclose the immediate payoff and the price source, but says nothing about irreversibility, what error occurs if item_id is not in the backpack, or whether the granted gold is returned in the response.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness5/5

Is the description appropriately sized, front-loaded, and free of redundancy?

Two compact sentences, zero filler, with the core action and effect front-loaded before the storage-box caveat. Every clause carries information.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness4/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

For a one-parameter mutation with no annotations and no output schema, the description covers purpose, payoff, price source, and the key prerequisite. The remaining gap is failure behavior and return shape, which is a moderate but not critical omission.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters3/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

The single parameter is fully documented in the schema ('背包内物品 id', 100% coverage), so baseline is 3. The description reinforces the backpack-only constraint but adds no format, range, or lookup hints beyond that.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

States a specific verb+resource ('出售背包里的物品') and the immediate effect ('立即获得金币'), which cleanly separates it from bpb_buy_item and the storage-related siblings. It even points to where the price lives (state.backpack.items[].sell_price), so an agent knows exactly what it is transacting on.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines4/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

Explicitly scopes usage to items currently in the backpack and names the alternative path for storage-box items ('需先 bpb_place_item 放回背包再出售'). That covers the main when/when-not decision an agent would face, though it offers no guidance on when selling is strategically appropriate.

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

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