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

Richly discloses behavior beyond the annotations: error semantics (404 no contract, 422 non-ERC-20, both uncharged), pricing ($0.003/call, first 25 free, failed calls free), and it explicitly reconciles the readOnlyHint=false annotation with the read-only nature ('not marked read-only because each call is charged'). This is exactly the kind of context annotations cannot carry.

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-loads purpose, then usage/alternative, then input constraints, then pricing, then annotation rationale. Dense but every clause earns its place; no filler or restatement of the name.

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 still enumerates return fields; it covers inputs, error cases, cost model, and usage routing. Nothing an agent needs to call it 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 coverage is 100%, so the schema already documents both parameters (baseline 3). The description adds the format constraint ('Both inputs are 0x addresses (40 hex characters)') and ties the token parameter to error behavior (no contract 404, non-ERC-20 422), which is meaningful semantic value 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?

Specific verb plus resource: 'Read one wallet's balance of one ERC-20 token on Polygon PoS', and it enumerates the returned fields (raw amount, decimals, symbol, human-readable amount). It also distinguishes itself from the native-coin sibling (polygon_balance) and implies distinction from polygon_token_info, so an agent can route correctly without opening schemas.

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?

Explicit when-to-use ('check stablecoin or token holdings before a transfer or trade') and names the alternative for the different case ('for the native coin use polygon_balance'). Conditions are stated, not left to inference.

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