existdb_validate_xquery

THE RISK

Low Risk

Why existdb_validate_xquery needs a policy

This tool performs syntax validation only—it parses and checks an XQuery expression against the database instance but does not execute the query, modify data, delete resources, or trigger side effects. It is purely informational (Read category). The severity is low because validation-only tools have minimal blast radius; the worst outcome would be false validation results.

From the tool's definition Tool name is 'existdb_validate_xquery' with description 'Validates the syntax of an XQuery expression against a live eXist-db instance'.

Documented attack patterns abuse exactly the kind of access existdb_validate_xquery gives an agent:

POLICY

How to control existdb_validate_xquery

PolicyLayer is an MCP gateway — it sits between your AI agents and Existdb, and nothing reaches the server without passing your rules. This is the rule we recommend for existdb_validate_xquery:

policy.json

{
  "version": "1",
  "default": "deny",
  "tools": {
    "existdb_validate_xquery": {}
  }
}

existdb_validate_xquery is read-only, so it stays allowed — but everything else on the server is denied unless you say otherwise.

Create a free account and register Existdb — nothing to install.
Add this policy — paste it, or build it visually.
Point your MCP client (Claude, Cursor, anything) at your gateway URL.

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EXPLORE

Related tools and policies

More Existdb tools

Destructive existdb_delete_resource Deletes a document or collection from eXist-db. Use with caution — deletion is permanent. Execute existdb_execute_query Executes an XQuery expression against a live eXist-db instance via the REST API Write existdb_store_document Stores (creates or replaces) an XML document in an eXist-db collection via PUT. Write existdb_create_collection Creates a new sub-collection inside an existing eXist-db collection. Read existdb_get_document Retrieves the XML content of a document stored in eXist-db. Read existdb_get_xquery_snippet Returns a ready-to-use XQuery code snippet for a common eXist-db programming pattern. Read existdb_list_collection Lists the contents of an eXist-db collection: sub-collections and XML documents Read existdb_list_namespace_functions Lists all documented functions in a given eXist-db / XQuery namespace.

All 12 Existdb tools →

Read tools on other servers

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Go deeper

The MCP Attack Database → Documented attack patterns against MCP deployments — and the policies that stop them.
Data exfiltration → How read access becomes an exfiltration channel when chained with untrusted content.
MCP token cost → What connecting this server costs in context-window tokens on every request.
Rate Limiting MCP Tool Calls: A Practical Guide →
MCP Security: Why Prompt Guardrails Aren't Enough →

FAQ

Questions about existdb_validate_xquery

What does the existdb_validate_xquery tool do? +

Validates the syntax of an XQuery expression against a live eXist-db instance. It is categorised as a Read tool in the Existdb MCP Server, which means it retrieves data without modifying state.

How do I enforce a policy on existdb_validate_xquery? +

Register the Existdb MCP server in PolicyLayer and add a rule for existdb_validate_xquery: allow, deny, rate-limit, or require approval. Point your MCP client at the PolicyLayer proxy URL and the rule is enforced on every call, before it reaches Existdb. Nothing to install.

What risk level is existdb_validate_xquery? +

existdb_validate_xquery is a Read tool with low risk. Read-only tools are generally safe to allow by default.

Can I rate-limit existdb_validate_xquery? +

Yes. Add a rate_limit block to the existdb_validate_xquery rule in your PolicyLayer policy. For example, setting max: 10 and window: 60 limits the tool to 10 calls per minute. Rate limits are tracked per agent session and reset automatically.

How do I block existdb_validate_xquery completely? +

Set action: deny in the PolicyLayer policy for existdb_validate_xquery. The AI agent will receive a policy violation error and cannot call the tool. You can also include a reason field to explain why the tool is blocked.

What MCP server provides existdb_validate_xquery? +

existdb_validate_xquery is provided by the Existdb MCP server (orazionelson/existdb-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.

Enforce policy on every Existdb tool call.

Start from Existdb, add the rest of your stack, and see everything your agents can call. Then put policy on all of it.

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