Scholar MCP Server

get_unpaywall_link_tool

Queries Unpaywall by DOI to retrieve a legal Open Access PDF link. Returns the URL or indicates a strict paywall.

Instructions

Checks the Unpaywall database using a DOI to find a legal Open Access PDF link. If found, returns the URL. If not, returns that it's behind a strict paywall.

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": "get_unpaywall_link_tool"
  }
}

Input Schema

Name	Required	Description	Default
`doi`	Yes

Output Schema

Name	Required	Description	Default
`result`	Yes

Schema Changelog

Changes observed during successful MCP inspections.

First observedv1.0.0Jul 28, 2026

TDQS

A4.8/5.0

Behavior5/5

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

No annotations are present, so the description carries full burden. It transparently describes the behavior: queries Unpaywall, returns URL if found, or states strict paywall. No side effects or contradictions.

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

Conciseness5/5

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

Two efficient sentences, front-loaded with the key action. No excess words or information.

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?

Given the single parameter and existence of an output schema, the description provides sufficient context for the tool's purpose and behavior. It covers input, process, and typical outputs.

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

Parameters5/5

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

The input schema has only one parameter (doi) with 0% coverage. The description explains that the DOI is used to query the Unpaywall database, adding crucial meaning beyond the schema.

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

Purpose5/5

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

The description clearly states the tool's function: it checks the Unpaywall database with a DOI to find a legal Open Access PDF link, and indicates success or paywall. It distinguishes from siblings like get_scihub_link_tool (illegal) and fetch_pdf_text_unpaywall_tool (fetches text).

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

Usage Guidelines4/5

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

The description implies when to use (when you have a DOI and want OA PDF), but does not explicitly mention when not to use or suggest alternatives like search_titles_unpaywall_tool for title-based search or get_scihub_link_tool for non-legal links.

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