FIXSIM

Send an Order Cancel Request

fixsim_cancel_order_out

Have FIXSIM send an Order Cancel Request (35=F) for an order it previously sent out with fixsim_send_order.

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": {
      "instance": "<instance>",
      "session": "<session>",
      "clOrdId": "<clOrdId>"
    },
    "name": "fixsim_cancel_order_out"
  }
}

Input Schema

Name	Required	Description
`apiKey`	No
`clOrdId`	Yes	ClOrdID of the order to cancel (becomes OrigClOrdID, tag 41)
`session`	Yes
`instance`	Yes
`newClOrdId`	No	New ClOrdID for the cancel request (tag 11); generated if omitted
`additionalTags`	No

Schema Changelog

Changes observed during successful MCP inspections.

First observedSep 12, 2026

TDQS

A3.5/5.0

Behavior3/5

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

Annotations only provide destructiveHint=false, and the description confirms it is an outbound FIXSIM request referencing a previously sent order. However, it discloses nothing about side effects, reversibility, permissions, or whether cancelling requires a live session.

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?

A single, well-formed sentence with the action and its precondition front-loaded. No filler or redundancy.

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

Completeness2/5

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

For a 6-parameter tool with low schema coverage, no output schema, and sparse annotations, the description is too thin. It omits any explanation of session/instance/auth handling needed to call the tool correctly.

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

Parameters2/5

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

Schema coverage is only 33%; clOrdId and newClOrdId are documented in the schema but session, instance, apiKey, and additionalTags are not. The description adds nothing to explain these undocumented parameters, referring only vaguely to 'an order it previously sent out'.

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 ('send an Order Cancel Request (35=F)') and ties it to a concrete precondition ('for an order it previously sent out with fixsim_send_order'). This clearly distinguishes it from siblings like fixsim_send_order and fixsim_act_on_orders.

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

Usage Guidelines3/5

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

The reference to fixsim_send_order implies the workflow context (cancel something you sent), but there is no explicit when/when-not guidance or comparison to alternatives such as fixsim_act_on_orders or sandbox_act_on_order. Usage is inferred, not stated.

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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