Tool Calling — ML Junction docs

Tool definitions use the standard function-tool shape. Supplying tools automatically makes tool support a required route capability unless you explicitly selected another requirement before validation.

{
  "model": "gpt-5.5",
  "messages": [
    {
      "role": "user",
      "content": "What is the weather in Kolkata?"
    }
  ],
  "tools": [
    {
      "type": "function",
      "function": {
        "name": "get_weather",
        "description": "Return current weather for a city.",
        "parameters": {
          "type": "object",
          "additionalProperties": false,
          "properties": {
            "city": { "type": "string" },
            "units": {
              "type": "string",
              "enum": ["metric", "imperial"]
            }
          },
          "required": ["city"]
        }
      }
    }
  ],
  "tool_choice": "auto",
  "requirements": {
    "tools": "required"
  }
}

Preserve tool_call_id when sending a tool result back to the model.. Keep assistant tool calls and their tool responses together during context truncation.. Use capabilities.parallel_tools when your agent requires multiple calls in one model turn.. Treat tool arguments as untrusted input and validate them against your own schema before execution.

Continue a reasoning tool loop

When the response reasoning.phase is awaiting_tool_results, keep the original assistant tool calls, their reasoning_details, and the continuation token. Execute every required tool, append one tool message per call ID, and send input_type=tool_results. Do not replace the full history with only the newest tool result unless your integration deliberately uses the specialized tool-results-only contract.

{
  "model": "gpt-5.5",
  "messages": [
    {
      "role": "user",
      "content": "Look up order 123 and tell me its status."
    },
    {
      "role": "assistant",
      "content": "",
      "tool_calls": [
        {
          "id": "call_order_123",
          "type": "function",
          "function": {
            "name": "lookup_order",
            "arguments": "{\"order_id\":\"123\"}"
          }
        }
      ],
      "reasoning_details": [
        {
          "type": "reasoning",
          "encrypted_content": "provider-opaque-state"
        }
      ]
    },
    {
      "role": "tool",
      "tool_call_id": "call_order_123",
      "content": "{\"status\":\"shipped\",\"eta\":\"2026-07-18\"}"
    }
  ],
  "reasoning": {
    "enabled": true,
    "continuation_token": "gwrt_v3.opaque-routing-ticket",
    "input_type": "tool_results",
    "pending_turn_action": "continue"
  },
  "tools": [
    {
      "type": "function",
      "function": {
        "name": "lookup_order",
        "description": "Look up an order by ID.",
        "parameters": {
          "type": "object",
          "additionalProperties": false,
          "properties": {
            "order_id": { "type": "string" }
          },
          "required": ["order_id"]
        }
      }
    }
  ]
}

Tool-loop problem · Gateway behavior · User action
Required result is missing · HTTP 409 PENDING_TOOL_LOOP with expected, supplied, and missing IDs · Wait for or supply every result, or explicitly Cancel/Fork
Unknown or duplicate result · Unsafe result is dropped and tool_history.dropped is returned · Fix the application mapping; inspect requested/effective IDs
Normal user text interrupts a pending loop · PENDING_TOOL_LOOP prevents accidental continuation · Choose Continue, Cancel, or Fork intentionally
Origin provider becomes unavailable · Native state is abandoned; eligible fallback receives portable visible history/tool messages · Accept the warning and fresh continuation state on success

Canonical URL: https://mljunction.com/docs/tools