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

Annotations declare the safety profile (not read-only, not destructive, not idempotent), and the description adds genuinely useful behavior beyond that: fill mechanics ('fills at the live YES/NO price, probability = price'), updown payout/resolution rules, 'zero fees', '24/7', and the auth requirement 'Agent key required'. It stops short of describing what a filled order returns or how partial fills/sells behave.

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?

The purpose and param template are front-loaded in the first sentence, with the updown detail following. It is dense and slightly run-on with stacked parentheticals, but nearly every clause carries operational information rather than 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?

For a 9-parameter mutation tool with no output schema and only 44% schema coverage, the description covers the core requirements (auth, fill semantics, updown rules) but leaves signal, competition, dry_run, and client_order_id entirely to the schema, and the venue enum conflict undermines trust in the parameter guidance. Adequate but with visible gaps.

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 only 44%, so the description must compensate, and it does add meaning for the required params ('market (question substring - or "next" for updown)', shares, side, action default buy). But it introduces a harmful inconsistency: the inline venue list is 'polymarket|kalshi|outcome|skew|txyz|updown' while the schema enum only permits polymarket|kalshi, which will mislead an agent about valid values.

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 names a specific verb (paper-trade / place order) and resource (prediction-market order on the agent book), and the sibling landscape (place_order, place_fx_order, place_perp_order, place_sports_bet) makes the market-type distinction meaningful. An agent can identify the correct tool without opening the 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?

It implicitly scopes usage by explaining the venue model and the updown special case ('pre-session entries at a flat $0.50... resolves off the Hyperliquid BTC mark'), and notes 'Agent key required'. However, it never explicitly states when to choose this over place_order or the other place_* siblings, nor any exclusions or prerequisites beyond the key requirement.

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