---
title: "Fix JSON-RPC error -32602: Invalid params (-32602)"
slug: "json-rpc-32602-invalid-params"
code: "-32602"
category: "Protocol & Serialization"
severity: "Medium"
canonical: "https://mcp-codex.com/errors/json-rpc-32602-invalid-params"
source: "MCP Codex (https://mcp-codex.com)"
dateModified: "2026-09-28"
---

# Fix JSON-RPC error -32602: Invalid params (-32602)

**Category**: Protocol & Serialization | **Severity**: Medium

## Symptom
Server rejects tool invocation stating arguments do not match schema.

## Root Cause
The AI model passed arguments with incorrect data types (e.g. string instead of integer or array), or omitted a required parameter defined in inputSchema.

## Remediation & Quick Fix
Inspect the tool's inputSchema with tools/list and ensure all required fields match their declared types.

## OS Remediation Commands

### MAC
```bash
# Inspect tool schema via MCP inspector:
npx @modelcontextprotocol/inspector
```

### WINDOWS
```bash
# Inspect tool schema via MCP inspector:
npx @modelcontextprotocol/inspector
```

### LINUX
```bash
# Inspect tool schema via MCP inspector:
npx @modelcontextprotocol/inspector
```

## Correct Configuration Example
```json
// Ensure payload arguments match required properties
{
  "jsonrpc": "2.0",
  "id": 12,
  "method": "tools/call",
  "params": {
    "name": "query_database",
    "arguments": {
      "limit": 10 // Number, not string "10"
    }
  }
}
```

## Canonical Diagnostic Link
https://mcp-codex.com/errors/json-rpc-32602-invalid-params

## Weekly Protocol & Patch Diffs
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