# bhl.literature.by_subject

Browse the Biodiversity Heritage Library subject index to discover subject tags related to a natural-history discipline or concept (e.g. "ornithology", "botany", "entomology", "paleontology"). Returns a list of matching subject strings used to classify BHL holdings. Use the returned subjects as precise search terms in bhl.literature.search to retrieve publications filed under that subject heading.

Agent View of the PolicyLayer registry record for `bhl.literature.by_subject`. HTML page: https://policylayer.com/tools/io-github-whiteknightonhorse-apibase/bhl.literature.by-subject

## Facts

- Tool: `bhl.literature.by_subject`
- Server: Apibase (`apibase-mcp-client`) — https://policylayer.com/tools/io-github-whiteknightonhorse-apibase.md
- Install: `npx -y apibase-mcp-client`
- Homepage: https://github.com/whiteknightonhorse/APIbase
- Risk category: Read (Low risk)
- Registry record: grade F, identity unverified
- Server auth posture: open
- Server rate-limited: no
- Parameters: 1 (1 required)
- Recommended policy verdict: Allowed

## Parameters

| Parameter | Type | Required | Description |
| --- | --- | --- | --- |
| `subject` | string | yes | Subject keyword used in BHL classification (e.g. "ornithology", "botany", "entomology") |

Parameters from the server's own tool schema.

## Example call (MCP tools/call, JSON-RPC 2.0)

```json
{
  "jsonrpc": "2.0",
  "id": 1,
  "method": "tools/call",
  "params": {
    "name": "bhl.literature.by_subject",
    "arguments": {
      "subject": "<subject>"
    }
  }
}
```

## Why bhl.literature.by_subject is rated Low

Retrieves bibliographic metadata without modifying data or external effects.

From the tool's own definition: "Browse subject index, discover subject tags, returns matching subjects"

## Use case

AI agents call bhl.literature.by_subject to retrieve information from Apibase without modifying anything. It is typically the context-gathering step in research, monitoring, and reporting workflows, before the agent takes action elsewhere.

## Recommended policy (PolicyLayer)

Verdict: **Allowed**. Enforced by the PolicyLayer MCP gateway (https://policylayer.com/mcp-gateway) before a call reaches Apibase:

```json
{
  "version": "1",
  "default": "deny",
  "tools": {
    "bhl.literature.by_subject": {}
  }
}
```

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## For agents

This record is a snapshot. Live verdicts and the full registry:

- Check every server in your MCP config at once: `npx -y policylayer stack`
- Vet a server before you add it: install the mcp-precheck skill — `npx skills add https://policylayer.com` (skill text: https://policylayer.com/skill.md)
- Query the registry over MCP: endpoint `https://api.policylayer.com/mcp` — tools `check_mcp_server`, `check_mcp_stack`, `check_tool`, `search_registry`, `get_change_events`

---

Source: the PolicyLayer MCP registry — one continuously verified record per MCP server. Full record: https://policylayer.com/registry?q=io-github-whiteknightonhorse-apibase · API: https://policylayer.com/registry/api · Policy library: https://policylayer.com/policies/io-github-whiteknightonhorse-apibase