# `europepmc__compare_citations`

Compare citations between two papers using an LLM (requires an LLM provider).

- Server: [Europe PMC](https://gateway.mcpharbor.dev/docs/servers/europepmc) (`dev.mcpharbor.gateway/europepmc`)
- Price per call: $0.0001 (100 micro-USD); only tools/call is charged
- Endpoint: `https://gateway.mcpharbor.dev/mcp` or `https://gateway.mcpharbor.dev/mcp/europepmc`
- Upstream tool: exposed by the provider; called through this gateway as `europepmc__compare_citations`
- Provider terms: <https://europepmc.org/Copyright> (verified 2026-09-19)
- Upstream API documentation: <https://europepmc.org/RestfulWebService>
- Rate limit: 500 requests per minute

## Parameters

- `pmid1` (string, required): PubMed ID of first paper
- `pmid2` (string, required): PubMed ID of second paper
- `task` (string, optional): Comparison task description Default: `Compare these two papers and their citations.`.

## Example call

Request headers and body:

```http
POST /mcp HTTP/1.1
Host: gateway.mcpharbor.dev
Authorization: Bearer <your gateway API key>
Content-Type: application/json
Accept: application/json, text/event-stream
MCP-Protocol-Version: 2026-07-28
Mcp-Method: tools/call
Mcp-Name: europepmc__compare_citations
```

```json
{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "_meta": {
      "io.modelcontextprotocol/clientCapabilities": {},
      "io.modelcontextprotocol/clientInfo": {
        "name": "example-agent",
        "version": "1.0.0"
      },
      "io.modelcontextprotocol/protocolVersion": "2026-07-28"
    },
    "arguments": {
      "pmid1": "example",
      "pmid2": "example"
    },
    "name": "europepmc__compare_citations"
  }
}
```

A successful response:

```json
{
  "id": 1,
  "jsonrpc": "2.0",
  "result": {
    "_meta": {
      "dev.mcpharbor.gateway/call": {
        "chargedMicroUsd": 100,
        "id": "<the id of this charge>"
      }
    },
    "content": [
      {
        "text": "<whatever the upstream tool returned>",
        "type": "text"
      }
    ],
    "resultType": "complete"
  }
}
```

This call costs $0.0001 (100 micro-USD). Reading this page and listing the tool cost nothing.
The `dev.mcpharbor.gateway/call` record in the result is the receipt for that charge. Each
POST is metered separately, so sending the same call again buys another one: see
[agent.txt](https://gateway.mcpharbor.dev/agent.txt), section 7, before retrying.

## Attribution

This provider asks for no attribution. Their terms still apply: see the table above.

## Tool definition

Exactly as `tools/list` returns it (free):

```json
{
  "_meta": {
    "dev.mcpharbor.gateway/pricing": {
      "currency": "USD",
      "pricePerCallMicroUsd": 100
    }
  },
  "annotations": {
    "openWorldHint": true,
    "readOnlyHint": true,
    "title": "Compare two papers' citations"
  },
  "description": "Compare citations between two papers using an LLM (requires an LLM provider).",
  "inputSchema": {
    "properties": {
      "pmid1": {
        "description": "PubMed ID of first paper",
        "title": "Pmid1",
        "type": "string"
      },
      "pmid2": {
        "description": "PubMed ID of second paper",
        "title": "Pmid2",
        "type": "string"
      },
      "task": {
        "default": "Compare these two papers and their citations.",
        "description": "Comparison task description",
        "title": "Task",
        "type": "string"
      }
    },
    "required": [
      "pmid1",
      "pmid2"
    ],
    "title": "compare_citationsArguments",
    "type": "object"
  },
  "name": "europepmc__compare_citations",
  "outputSchema": {
    "additionalProperties": true,
    "title": "compare_citationsDictOutput",
    "type": "object"
  }
}
```