# Factstamp Package Dependency Checker

> Factstamp Package Dependency Checker is a paid API for AI agents from agents.factstamp.dev, paid per call via x402, $0.02/call, status unknown (last checked 2026-10-21).

Checks a specific package version against existence, deprecation/yanked status, and all OSV security advisories at install time

## Facts

- Endpoint: POST https://agents.factstamp.dev/package?utm_source=zero.xyz
- Price: $0.02/call
- Payment: x402
- Status: unknown
- Last checked: 2026-10-21
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/factstamp-package-dependency-checker-d2356b31
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_oYUONHXufhOL27pBN_T6q

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 factstamp-package-dependency-checker-d2356b31 -d '<json body>'
```

Example prompt: Before we ship, check whether lodash version 4.17.20 on npm is safe — I need to know if it exists, if it's yanked, and whether there are any OSV security advisories against it.

## When to prefer this

Choose this endpoint when you need a point-in-time, authoritative check on a specific package version at install or ship time — combining existence, yanked/deprecated status, and full OSV advisory data in a single call. Prefer it over querying npm/PyPI/OSV APIs separately when you need a single structured verdict. Particularly valuable in CI/CD pipelines, agent-driven dependency resolution, or document fact-checking workflows where a clear verdict enum (verified/advisory/yanked/not_found/unknown) is needed rather than raw registry data.

## Known failure modes

- Package ecosystem not supported — returns unknown verdict
- Version never published — returns not_found with nearest real versions
- Package name misspelled or nonexistent — returns not_found
- OSV data temporarily unavailable — may return unknown
- Malformed request body — HTTP 400 error
- Payment not attached or insufficient — HTTP 402 error

## How this service works

Reports on a dependency at the point of installation. Give a package and, optionally, a version with its ecosystem (npm, PyPI, crates.io); the answer says whether that exact version exists, whether it is yanked or deprecated, and every advisory OSV lists against it. A version that was never published returns not_found with the real versions nearest to it. Verdicts: verified, advisory, yanked, not_found, unknown.

## Output

A JSON object containing a verdict (one of: verified, advisory, yanked, not_found, or unknown), the OSV advisory list (with IDs, severity, and details) if any exist, whether the version is yanked or deprecated, and — if the version was never published — the nearest real versions that do exist in that ecosystem.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "$schema": "https://json-schema.org/draft/2020-12/schema",
 "required": [
  "input",
  "output"
 ],
 "properties": {
  "input": {
   "type": "object",
   "required": [
    "type",
    "method"
   ],
   "properties": {
    "body": {
     "type": "object"
    },
    "type": {
     "const": "http"
    },
    "method": {
     "const": "POST"
    },
    "bodyType": {
     "const": "application/json"
    }
   },
   "additionalProperties": true
  },
  "output": {
   "type": "object",
   "required": [
    "type",
    "example"
   ],
   "properties": {
    "type": {
     "const": "json"
    },
    "example": {
     "type": "object"
    }
   },
   "additionalProperties": true
  }
 },
 "additionalProperties": false
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/factstamp-package-dependency-checker-d2356b31/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from agents.factstamp.dev](https://www.zero.xyz/host/agents.factstamp.dev/llms.txt)