oddsrail

place_order

Destructive

Submit a limit order for a prediction market, specifying side, price, size, and token. Includes dry-run mode and post-only option for safer execution.

Instructions

Place a limit order. DRY-RUN by default: returns the order it would post. Real trading needs ODDSRAIL_DRY_RUN=0 and POLYMARKET_PRIVATE_KEY. The operator's builder code is signed into the order. price is the implied probability in (0,1); size is in SHARES (notional = price * size), and the exchange enforces a $1 minimum notional on marketable orders. post_only=True rejects rather than crosses the book.

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": {
      "token_id": "<token_id>",
      "side": "<side>",
      "price": "<price>",
      "size": "<size>"
    },
    "name": "place_order"
  }
}

Input Schema

Name	Required	Description	Default
`side`	Yes
`size`	Yes
`price`	Yes
`token_id`	Yes
`post_only`	No

Schema Changelog

Changes observed during successful MCP inspections.

Changed3 schema fields changedv0.18.1Sep 22, 2026

removedInput schema / properties / order_type

Removed value: -{
-  "default": "GTC",
-  "title": "Order Type",
-  "type": "string"
-}

addedInput schema / properties / post_only

Added value: +{
+  "default": false,
+  "title": "Post Only",
+  "type": "boolean"
+}

changedOutput schema / (root)

Previous value: -{
-  "properties": {
-    "result": {
-      "title": "Result",
-      "type": "string"
-    }
-  },
-  "required": [
-    "result"
-  ],
-  "title": "place_orderOutput",
-  "type": "object"
-}New value: +null

First observedv0.3.0Aug 24, 2026

TDQS

A4.4/5.0

Behavior5/5

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

Beyond annotations that already mark this as destructive and non-read-only, the description discloses dry-run default behavior, signed builder code, post_only rejection semantics, and the exchange's $1 minimum notional. This materially enriches the agent's understanding of side effects and execution behavior, with no contradiction of the annotations.

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?

Three dense sentences pack the essential behavioral and parameter information with no filler. The dry-run warning is front-loaded, and the parameter clarifications are grouped logically, making the description easy to scan.

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?

The description covers the key runtime behavior, prerequisites, order semantics, and constraints for a trading tool. It lacks an explicit return shape or error behavior, but the statement 'returns the order it would post' gives a sufficient baseline, and annotations already signal risk.

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?

With 0% schema description coverage, the description must carry the burden. It does well for price (implied probability in (0,1)), size (shares), notional calculation, and post_only, but leaves the required 'side' and 'token_id' parameters unexplained. This is a clear gap for such a consequential tool.

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?

The description opens with a specific verb and resource: 'Place a limit order.' It immediately establishes scope by mentioning Polymarket's private key, which distinguishes it from the Kalshi-specific sibling 'kalshi_place_order.' The dry-run default further sharpens what the tool does.

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?

The description clearly states the default dry-run behavior and the exact environment variables required for real trading, giving the agent concrete conditions for when actual side effects occur. It does not explicitly name alternatives or say when not to use the tool, but the context is sufficient for most routing decisions.

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