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

Annotations already declare readOnlyHint/destructiveHint=false, and the description reinforces it with 'reads or computes only and changes nothing'. Beyond that it discloses the commercial behavior an agent cannot see anywhere else: $0.01/call via x402 or a card key, first 25 free, failed calls free, and that repeats are billed because nothing is cached.

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 what the call returns, then the input modes, then use cases, then pricing — a sensible order with no filler. The pricing sentence is long and packed with three separate facts in one clause, which slightly slows scanning but every element earns its place.

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?

There is no output schema, but the description enumerates the returned fields (bids, asks, best bid/ask, mid, spread, depth within 5 cents), the level cap, and the outcome selection rule, so an agent knows what it will get. Payment, safety, and caching behavior are all covered, leaving nothing material for a call decision unstated.

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 description coverage is 100%, so the schema already documents all four parameters, and this sets the baseline at 3. The description adds only a concrete example slug value and frames slug+outcome as an alternative to token_id, which the schema already states with 'Instead of slug'.

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?

States a specific verb and resource: bids/asks up to 50 levels, best bid/ask, mid, spread, and USD depth within 5 cents of mid for one market outcome. The contrast with 'the last trade' price hints at the difference from polymarket_price_history, but no sibling is named explicitly, so an agent must infer the boundary.

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 concrete when-to-use contexts — checking liquidity and slippage before a trade, or getting a sharper price than the last trade — and explains the two mutually exclusive input routes (slug+outcome vs token_id). It does not state when to prefer polymarket_price_history or polymarket_markets instead, leaving that routing to inference.

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