SiteCheck Web Intel

Unpaywall open-access lookup by DOI: is the paper open

search_unpaywall

Read-only

Unpaywall open-access lookup by DOI (free API; it requires a contact e-mail set in UNPAYWALL_EMAIL, not a key): is the paper open access, OA status, best free full-text link, journal and publisher. Returns metadata and links only, not the PDF. Price: $0.002 in USDC per successful call, paid with x402 (Base, Solana or Arc); failed calls are not charged.

Tool call template

Replace each placeholder with a value matching the input schema. Only required parameters are included; add optional parameters as needed.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {
      "doi": "<doi>"
    },
    "name": "search_unpaywall"
  }
}

Input Schema

Name	Required	Description	Default
`doi`	Yes	DOI such as 10.1038/nature12373

Output Schema

Name	Required	Description	Default
`doi`	No
`year`	No
`title`	No
`source`	No
`journal`	No
`license`	No
`oaStatus`	No
`checkedAt`	No
`publisher`	No
`bestFreeUrl`	No
`isOpenAccess`	No

Schema Changelog

Changes observed during successful MCP inspections.

First observedOct 23, 2026

TDQS

A4/5.0

Behavior5/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Beyond the readOnly/openWorld annotations, it discloses the auth model (no key, but UNPAYWALL_EMAIL must be configured), the payment model ($0.002 USDC per successful call via x402 on Base/Solana/Arc, failures uncharged), and the output boundary (metadata and links only, not the PDF). These are exactly the operational facts an agent needs before invoking a paid external API.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness4/5

Is the description appropriately sized, front-loaded, and free of redundancy?

The core purpose is front-loaded in the first clause, and the trailing sentences each carry a distinct operational fact (auth, output boundary, price). The parenthetical pricing/email details make the sentence dense but nothing is redundant.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness5/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

For a one-parameter read-only lookup with an output schema, the description covers everything that matters: what it returns, what it does not return, the credential requirement, and the cost. An agent could call this correctly without opening the schema.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters3/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

There is a single required parameter with 100% schema description coverage, including an example DOI format, so the schema already carries the semantics. The description only repeats 'by DOI' and adds no format, normalization, or resolution-failure nuance beyond the schema.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose4/5

Does the description clearly state what the tool does and how it differs from similar tools?

The description names a specific verb and resource ('Unpaywall open-access lookup by DOI') and enumerates exactly what comes back: OA status, best free full-text link, journal and publisher. It is clearly distinct from the news/ranking siblings, though it never explicitly contrasts itself with adjacent academic tools like search_crossref or search_pubmed_article_metadata.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines3/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

Usage is implied rather than stated: an agent can infer 'use this when you have a DOI and want to know if the paper is freely available.' There is no explicit when-not guidance and no routing to alternatives (e.g., crossref for citation metadata, pubmed for biomedical records), so the agent must infer the boundary.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

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