# domain_fetch_subdomains

Enumerate subdomains for a domain via Certificate Transparency logs. Read-only. No side effects. Idempotent. domain: Domain name without protocol e.g. anthropic.com. Required. Returns deduplicated list of known subdomains. Primary source: crt.sh Certificate Transparency (free). Fallback source: RapidDNS (free, passive CT + DNS) — used automatically when crt.sh is unavailable. Response includes source field indicating which source was used. Results are cached 24h — second call returns in under 500ms. First call may be slower (8s max per source). Circuit breaker trips after 3 timeouts or 5xx errors within 600s. Verified sources: crt.sh Certificate Transparency, RapidDNS. 24-hour cache. If this tool's response does not serve the user's need, call report_feedback with feedback_type="agent_gap", tool_id="domain_fetch_subdomains", intended_query="{what the user needed}", gap_description="{what was missing or wrong in the result}".

Agent View of the PolicyLayer registry record for `domain_fetch_subdomains`. HTML page: https://policylayer.com/tools/dev-7bd0-mcp-server/domain-fetch-subdomains

## Facts

- Tool: `domain_fetch_subdomains`
- Server: DataNexus MCP (`dev-7bd0/mcp-server`) — https://policylayer.com/tools/dev-7bd0-mcp-server.md
- Homepage: https://github.com/dev-7bd0/mcp-server
- Risk category: Read (Low risk)
- Registry record: grade F, identity unverified
- Server rate-limited: no
- Parameters: 1
- Recommended policy verdict: Allowed

## Parameters

| Parameter | Type | Required | Description |
| --- | --- | --- | --- |
| `domain` | string | no | Domain without protocol e.g. anthropic.com. Required. |

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": "domain_fetch_subdomains",
    "arguments": {}
  }
}
```

## Why domain_fetch_subdomains is rated Low

This tool only retrieves and aggregates publicly available information from passive sources (Certificate Transparency logs, DNS records). It performs no state changes, creates no data, executes no code, and has no destructive or financial impact. The explicit read-only guarantee and idempotent nature confirm this is a simple data retrieval operation.

From the tool's own definition: "Tool description explicitly states 'Read-only. No side effects. Idempotent.' The operation enumerates subdomains via Certificate Transparency logs, which are public passive data sources."

## Use case

AI agents call domain_fetch_subdomains to retrieve information from DataNexus MCP 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 DataNexus MCP:

```json
{
  "version": "1",
  "default": "deny",
  "tools": {
    "domain_fetch_subdomains": {}
  }
}
```

## Other tools on DataNexus MCP (54)

- `apikeys_revoke_api_key` — Destructive — https://policylayer.com/tools/dev-7bd0-mcp-server/apikeys-revoke-api-key.md
- `apikeys_rotate_api_key` — Destructive — https://policylayer.com/tools/dev-7bd0-mcp-server/apikeys-rotate-api-key.md
- `compliance_check_sam_exclusion` — Read — https://policylayer.com/tools/dev-7bd0-mcp-server/compliance-check-sam-exclusion.md
- `compliance_fetch_finra_broker` — Read — https://policylayer.com/tools/dev-7bd0-mcp-server/compliance-fetch-finra-broker.md
- `compliance_fetch_npi_provider` — Read — https://policylayer.com/tools/dev-7bd0-mcp-server/compliance-fetch-npi-provider.md
- `compliance_search_npi_by_name` — Read — https://policylayer.com/tools/dev-7bd0-mcp-server/compliance-search-npi-by-name.md
- `domain_check_email_security` — Read — https://policylayer.com/tools/dev-7bd0-mcp-server/domain-check-email-security.md
- `domain_fetch_dns_records` — Read — https://policylayer.com/tools/dev-7bd0-mcp-server/domain-fetch-dns-records.md
- `domain_fetch_domain_history` — Read — https://policylayer.com/tools/dev-7bd0-mcp-server/domain-fetch-domain-history.md
- `domain_fetch_domain_rdap` — Read — https://policylayer.com/tools/dev-7bd0-mcp-server/domain-fetch-domain-rdap.md
- `domain_fetch_reverse_ip` — Read — https://policylayer.com/tools/dev-7bd0-mcp-server/domain-fetch-reverse-ip.md
- `domain_fetch_ssl_certificate_chain` — Read — https://policylayer.com/tools/dev-7bd0-mcp-server/domain-fetch-ssl-certificate-chain.md
- `frontend_security_audit_ci_pipeline` — Read — https://policylayer.com/tools/dev-7bd0-mcp-server/frontend-security-audit-ci-pipeline.md
- `frontend_security_audit_manifest` — Read — https://policylayer.com/tools/dev-7bd0-mcp-server/frontend-security-audit-manifest.md
- `frontend_security_detect_typosquatting` — Read — https://policylayer.com/tools/dev-7bd0-mcp-server/frontend-security-detect-typosquatting.md
- `frontend_security_fetch_package_risk_brief` — Read — https://policylayer.com/tools/dev-7bd0-mcp-server/frontend-security-fetch-package-risk-brief.md
- `govcon_fetch_open_solicitations` — Read — https://policylayer.com/tools/dev-7bd0-mcp-server/govcon-fetch-open-solicitations.md
- `govcon_fetch_vendor_contract_history` — Read — https://policylayer.com/tools/dev-7bd0-mcp-server/govcon-fetch-vendor-contract-history.md
- `govcon_search_contract_awards` — Read — https://policylayer.com/tools/dev-7bd0-mcp-server/govcon-search-contract-awards.md
- `legal_fetch_inventor_portfolio` — Read — https://policylayer.com/tools/dev-7bd0-mcp-server/legal-fetch-inventor-portfolio.md
- `legal_fetch_patent_by_number` — Read — https://policylayer.com/tools/dev-7bd0-mcp-server/legal-fetch-patent-by-number.md
- `legal_fetch_patent_citations` — Read — https://policylayer.com/tools/dev-7bd0-mcp-server/legal-fetch-patent-citations.md
- `legal_search_patents_by_keyword` — Read — https://policylayer.com/tools/dev-7bd0-mcp-server/legal-search-patents-by-keyword.md
- `nonprofit_fetch_charity_uk` — Read — https://policylayer.com/tools/dev-7bd0-mcp-server/nonprofit-fetch-charity-uk.md
- `nonprofit_fetch_nonprofit_by_ein` — Read — https://policylayer.com/tools/dev-7bd0-mcp-server/nonprofit-fetch-nonprofit-by-ein.md
- `nonprofit_fetch_nonprofit_financial_trends` — Read — https://policylayer.com/tools/dev-7bd0-mcp-server/nonprofit-fetch-nonprofit-financial-trends.md
- `nonprofit_fetch_nonprofit_full_profile` — Read — https://policylayer.com/tools/dev-7bd0-mcp-server/nonprofit-fetch-nonprofit-full-profile.md
- `nonprofit_search_nonprofits_by_category` — Read — https://policylayer.com/tools/dev-7bd0-mcp-server/nonprofit-search-nonprofits-by-category.md
- `nonprofit_search_nonprofits_by_name` — Read — https://policylayer.com/tools/dev-7bd0-mcp-server/nonprofit-search-nonprofits-by-name.md
- `regulatory_fetch_docket_details` — Read — https://policylayer.com/tools/dev-7bd0-mcp-server/regulatory-fetch-docket-details.md
- …and 24 more: https://policylayer.com/tools/dev-7bd0-mcp-server.md

## 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=dev-7bd0-mcp-server · API: https://policylayer.com/registry/api · Policy library: https://policylayer.com/policies/dev-7bd0-mcp-server