# X402 Delivery Size Check

> X402 Delivery Size Check is a paid API for AI agents from api.delx.ai, paid per call via x402, $0.001/call, status unknown (last checked 2026-09-13).

Checks whether a serialized agent result's byte size falls within a buyer-specified maximum, returning acceptance or rejection status with mismatch reasons.

## Facts

- Endpoint: POST https://api.delx.ai/api/v1/x402/x402-delivery-size-check
- Price: $0.001/call
- Payment: x402
- Status: unknown
- Last checked: 2026-09-13
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/x402-delivery-size-check-879a2e73
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_VFzZ8gV81TqzBSna70lp3

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 x402-delivery-size-check-879a2e73 -d '<json body>'
```

Example prompt: Before we pay for this agent delivery, check whether the result object fits within a 10000-byte limit — I want to know if it's accepted or rejected and why.

## When to prefer this

Use this endpoint when you need a deterministic, in-memory byte-size check against a buyer-specified limit before accepting or paying for an x402 or agentic marketplace delivery. Prefer it over custom client-side size checks when you need a normalized, versioned evidence record and explicit acceptance/rejection reasoning suitable for dispute resolution or audit trails.

## Known failure modes

- Result object has more than 128 properties (maxProperties exceeded), causing a validation error
- maximum_bytes not provided or non-integer, returning a parameter error
- Result cannot be serialized (circular references or non-serializable values), causing a processing error
- Byte size exactly at boundary may return edge-case acceptance depending on comparison operator semantics

## How this service works

X402 Delivery Size Check: X402 Delivery Size Check checks serialized result byte size against a buyer limit from bounded caller-supplied values without an external provider. Call X402 Delivery Size Check before paying for or accepting an x402 or agent delivery assembled from caller-supplied challenge and result metadata. Returns contract-specific checks, normalized evidence, mismatch reasons, and an explicit acceptance or rejection status for X402 Delivery Size Check as versioned deterministic…

## Output

Returns an explicit acceptance or rejection status, the measured byte size of the serialized result, any mismatch reasons explaining why the limit was exceeded, and normalized evidence — all computed deterministically in memory without external calls or data retention.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "properties": {
  "result": {
   "type": "object",
   "description": "Result supplied to X402 Delivery Size Check; used only for this bounded calculation and processed in memory without retention.",
   "maxProperties": 128,
   "additionalProperties": true
  },
  "maximum_bytes": {
   "type": "integer",
   "description": "Maximum Bytes supplied to X402 Delivery Size Check; used only for this bounded calculation and processed in memory without retention."
  }
 }
}
```

## Response schema (JSON Schema)

```json
{
 "type": "json",
 "example": {
  "result": {
   "bytes": 39,
   "within_budget": true
  },
  "schema": "delx/util-x402-delivery-size-check/v1",
  "status": "pass",
  "evidence": {
   "retained": false,
   "input_sha256": "076621b47df3f39c3106d66269581bbf20cc78094ab64cec4fdb10ac2b5f03d1",
   "external_calls": 0
  },
  "operation": "delivery_contract:x402_delivery_size_check"
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/x402-delivery-size-check-879a2e73/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from api.delx.ai](https://www.zero.xyz/host/api.delx.ai/llms.txt)