# Content Length Check

> Content Length Check is a paid API for AI agents from api.delx.ai, paid per call via x402, $0.001/call, status unknown (last checked 2026-09-15).

Compares a declared Content-Length header value against an observed byte count and returns a deterministic pass/advisory verdict with normalized evidence.

## Facts

- Endpoint: POST https://api.delx.ai/api/v1/x402/content-length-check
- Price: $0.001/call
- Payment: x402
- Status: unknown
- Last checked: 2026-09-15
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/content-length-check-d685c369
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_brzJk_NA4tRe-4vGnaIYZ

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 content-length-check-d685c369 -d '<json body>'
```

Example prompt: Check whether the declared Content-Length of 2048 matches the observed byte count of 1984 — tell me if it passes or if there's a mismatch I should worry about.

## When to prefer this

Use this endpoint when an AI agent needs a stateless, auditable, deterministic check that a Content-Length HTTP header matches the actual observed byte count before accepting, caching, redirecting, or retrying a web response. Prefer it over manual comparison when you need a versioned JSON record of the finding for audit trails or when operating in an agentic pipeline that requires explicit pass/advisory signals.

## Known failure modes

- Missing or null declared/observed integers cause a validation error
- Non-integer values for declared or observed fields are rejected
- Negative byte counts may trigger an invalid-input error
- Payment failure via x402 prevents the call from completing

## How this service works

Content Length Check: Content Length Check compares declared Content-Length with an observed byte count from bounded caller-supplied values without an external provider. Call Content Length Check before accepting, caching, redirecting, or retrying a caller-supplied web response. Returns normalized web evidence, the computed finding, and an explicit pass or advisory status for Content Length Check as versioned deterministic JSON. Price: $0.001 USDC via x402 on Base. First-party, stateless, memor…

## Output

Returns versioned deterministic JSON containing: normalized web evidence (declared and observed values), the computed finding (difference and match status), and an explicit pass or advisory status indicating whether the declared Content-Length matches the observed byte count.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "properties": {
  "declared": {
   "type": "integer",
   "description": "Declared supplied to Content Length Check; used only for this bounded calculation and processed in memory without retention."
  },
  "observed": {
   "type": "integer",
   "description": "Observed supplied to Content Length Check; used only for this bounded calculation and processed in memory without retention."
  }
 }
}
```

## Response schema (JSON Schema)

```json
{
 "type": "json",
 "example": {
  "result": {
   "delta": 0,
   "matched": true,
   "declared": 128,
   "observed": 128
  },
  "schema": "delx/util-content-length-check/v1",
  "status": "pass",
  "evidence": {
   "retained": false,
   "input_sha256": "c55f65a8b217d1823723eaaef27fb2baf48c4cfd7f20ccc0fecf75ec925d4da5",
   "external_calls": 0
  },
  "operation": "web_reliability:content_length_check"
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/content-length-check-d685c369/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)