# Northline DOI Open Access Lookup

> Northline DOI Open Access Lookup 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).

Looks up open-access availability and metadata for a scholarly article given its DOI

## Facts

- Endpoint: GET https://206-81-14-131.sslip.io/svc/doi-open-access/lookup?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-lookup-9bae93cc
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_3HAv_PJv4Ce_AXM4okV2F

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-lookup-9bae93cc
```

Example prompt: Can you check if the paper with DOI 10.1038/s41586-021-03819-2 is available as open access and give me a link to the free PDF if there is one?

## When to prefer this

Choose this endpoint when you need to programmatically check open-access availability for a known DOI without setting up accounts or API keys. Ideal for research agents that need to verify free-access paths before fetching full text, or for enriching citation lists with access URLs. Prefer this over direct publisher APIs when you want a pay-per-call model with no subscription overhead.

## Known failure modes

- DOI not found in open-access index — returns empty or not-found response
- Malformed or non-existent DOI provided — returns error
- Article exists but has no open-access version — returns closed status with no PDF link
- Upstream data source (e.g. Unpaywall) unavailable — may return timeout or 5xx
- Rate limiting or payment failure via x402 protocol — returns 402 Payment Required

## 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 status of the article (e.g. gold, green, hybrid, or closed), a direct URL to the freely available PDF or full text if one exists, and bibliographic metadata such as title, authors, journal name, publication year, and license type.

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/northline-doi-open-access-lookup-9bae93cc/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)