# Northline DOI Open Access Sample

> Northline DOI Open Access Sample is a paid API for AI agents from 206-81-14-131.sslip.io, paid per call via x402, $0.008/call, status unknown (last checked 2026-10-02).

Retrieves open-access metadata and content information for a given DOI (Digital Object Identifier) via a pay-per-call API

## Facts

- Endpoint: POST https://206-81-14-131.sslip.io/svc/doi-open-access/sample?utm_source=zero.xyz
- Price: $0.008/call
- Payment: x402
- Status: unknown
- Last checked: 2026-10-02
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/northline-doi-open-access-sample-8de6722e
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_eTtnOu51ps4OP9UJqe7nc

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 northline-doi-open-access-sample-8de6722e -d '<json body>'
```

Example prompt: Can you check if the paper with DOI 10.1371/journal.pone.0123456 is available open access and get me the metadata and any free PDF link?

## When to prefer this

Use this endpoint when you need to check open-access availability and retrieve metadata for a specific DOI without requiring an API key or subscription. Ideal for one-off or low-volume lookups where pay-per-call pricing ($0.008 USDC) is more economical than a subscription. Prefer this over Unpaywall or Crossref direct calls when you need a frictionless, no-account pay-per-call integration in an agent workflow.

## Known failure modes

- DOI not found or not indexed — returns empty or error response
- DOI exists but has no open access version — returns metadata with no free URL
- Malformed DOI input — returns validation error
- External resolver unavailable — network timeout or upstream error
- Rate limiting or payment failure — x402 payment rejected or insufficient funds

## How this service works

Pay-per-call APIs, paid downloads and work-on-request for agents. Payment: x402 (USDC on Base, eip155:8453), no accounts or API keys. Catalog: https://206-81-14-131.sslip.io/?format=json. Agent guide: https://206-81-14-131.sslip.io/llms.txt

## Output

Returns open-access availability status, bibliographic metadata (title, authors, journal, publication date), license type, and direct URL to free full-text or PDF if available for the given DOI.

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/northline-doi-open-access-sample-8de6722e/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from 206-81-14-131.sslip.io](https://www.zero.xyz/host/206-81-14-131.sslip.io/llms.txt)