# Network Calc MTU/MSS Calculator

> Network Calc MTU/MSS Calculator is a paid API for AI agents from network-calc.x402tookit.com, paid per call via x402, $0.02/call, status unknown (last checked 2026-10-29).

Calculates TCP MSS from a given MTU for IPv4/IPv6, computes effective MTU through tunnels (PPPoE, GRE, VXLAN, WireGuard, etc.), and counts IPv4 fragments for a payload size.

## Facts

- Endpoint: GET https://network-calc.x402tookit.com/mtu-mss?utm_source=zero.xyz
- Price: $0.02/call
- Payment: x402
- Status: unknown
- Last checked: 2026-10-29
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/network-calc-mtu-mss-calculator-7e3e14a9
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_uxKFqzIReMhNEsz4FXQiQ

Status and success rate cover calls made through Zero and Zero's own probes. Third-party monitors may report differently.

## How to call it through Zero

Zero handles the 402 payment challenge and records the run. With the Zero CLI installed (`npm i -g @zeroxyz/cli`):

```sh
zero fetch --capability network-calc-mtu-mss-calculator-7e3e14a9
```

Example prompt: What is the TCP MSS and effective MTU for a WireGuard-over-IPv4 tunnel on a standard 1500-byte Ethernet link, using IPv4 with TCP timestamps enabled?

## When to prefer this

Use this endpoint when you need precise TCP MSS values for a specific MTU and tunnel combination, particularly when configuring firewall MSS clamping rules, diagnosing TCP black-hole issues through tunnels, or calculating IPv4 fragment counts for large UDP payloads. It covers a wide range of tunnel types (PPPoE, GRE, VXLAN, WireGuard, MPLS, etc.) and handles both IPv4 and IPv6, making it more specialized and accurate than manual header-subtraction calculations.

## Known failure modes

- Missing required 'mtu' parameter returns a validation error
- Invalid tunnel enum value returns a 400 bad request
- MTU value below minimum (e.g. below 68 for IPv4) may return an error or edge-case result
- Requesting IPv6 fragmentation counts may return a not-applicable note since IPv6 does not fragment in transit
- Malformed query parameters return schema validation errors

## How this service works

TCP MSS from an MTU for IPv4 or IPv6, effective MTU through tunnels (PPPoE, GRE, VXLAN, WireGuard) and IPv4 fragment counts.

## Output

Returns the computed TCP MSS in bytes, the effective MTU after tunnel overhead deductions, the recommended MSS clamp value, fragmentation details (fragment count, per-fragment payload bytes, total IP bytes) when a payload size is provided, a human-readable summary, tunnel-specific notes, and any warnings or reasons behind the computed values.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "$schema": "https://json-schema.org/draft/2020-12/schema",
 "required": [
  "input"
 ],
 "properties": {
  "input": {
   "type": "object",
   "required": [
    "type",
    "method"
   ],
   "properties": {
    "type": {
     "type": "string",
     "const": "http"
    },
    "method": {
     "enum": [
      "GET"
     ],
     "type": "string"
    },
    "queryParams": {
     "type": "object",
     "required": [
      "mtu"
     ],
     "properties": {
      "mtu": {
       "type": "integer",
       "description": "Link MTU in bytes (the IP packet size, 1500 for Ethernet)"
      },
      "tunnel": {
       "enum": [
        "none",
        "pppoe",
        "gre",
        "gre-ipv6",
        "ipip",
        "vxlan",
        "geneve",
        "wireguard-ipv4",
        "wireguard-ipv6",
        "mpls"
       ],
       "type": "string",
       "description": "Encapsulation: none, pppoe, gre, gre-ipv6, ipip, vxlan, geneve, wireguard-ipv4, wireguard-ipv6, mpls (default none)"
      },
      "ipVersion": {
       "type": "integer",
       "description": "4 (default) or 6"
      },
      "payloadBytes": {
       "type": "integer",
       "description": "IPv4 payload to send, to count fragments (UDP datagram incl. 8-byte header, or any IP payload)"
      },
      "tcpTimestamps": {
       "type": "string",
       "description": "true: TCP timestamp option (12 bytes) is in use"
      }
     }
    }
   },
   "additionalProperties": false
  },
  "output": {
   "type": "object",
   "required": [
    "type"
   ],
   "properties": {
    "type": {
     "type": "string"
    },
    "example": {
     "type": "object",
     "properties": {
      "mtu": {
       "type": [
        "null",
        "number"
       ]
      },
      "asOf": {
       "type": [
        "null",
        "string"
       ]
      },
      "source": {
       "type": [
        "null",
        "string"
       ]
      },
      "tunnel": {
       "type": [
        "null",
        "string"
       ]
      },
      "reasons": {
       "type": [
        "array",
        "null"
       ],
       "items": {
        "type": "string"
       }
      },
      "summary": {
       "type": [
        "null",
        "string"
       ]
      },
      "verdict": {
       "type": [
        "null",
        "string"
       ]
      },
      "degraded": {
       "type": [
        "boolean",
        "null"
       ]
      },
      "mssBytes": {
       "type": [
        "null",
        "number"
       ]
      },
   
… (truncated)
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/network-calc-mtu-mss-calculator-7e3e14a9/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from network-calc.x402tookit.com](https://www.zero.xyz/host/network-calc.x402tookit.com/llms.txt)