filter

Test if a Nostr event matches a given filter. Returns true or false.

SERVERNostr Bray SOURCEnostr-bray

Low RISK CLASS

Category Read

Parameters 00 required

Recommended Allowedsee the rule below

Registry record Grade F, identity unverified Pull the record →

This record as markdown: /tools/dev-forgesworn-bray/filter.md

WHAT IT DOES

What filter does on Nostr Bray

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

RISK

Why filter is rated Low

This tool performs a conditional check against a Nostr event without creating, modifying, deleting, or executing any external operations. It is purely informational—testing whether an event meets criteria and returning a boolean result. This is consistent with the Read category (retrieves or queries data; no side effects).

From the tool's definition Tool name 'filter' with description 'Test if a Nostr event matches a given filter. Returns true or false.' — the verb 'test' and 'returns true or false' indicate a query/evaluation operation with no side effects.

Attacks that exploit this kind of access

RECOMMENDED RULE

The rule that runs filter safely

PolicyLayer is an MCP gateway: it sits between your AI agents and Nostr Bray, and checks every tool call against a rule you set before the call runs. Nothing changes on the server itself. For filter, this is the rule to start with:

filter Allowed

filter is read-only, so it stays allowed. Everything else on the server is denied unless you say otherwise.

View as policy code

policy.json

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

ALLOW ONLY THIS TOOL → Instant setup, no code required.

The button opens the PolicyLayer dashboard: create your workspace, connect Nostr Bray, apply this rule, and every filter call is checked against it from then on.

FAQ

Questions about filter

What does the filter tool do? +

Test if a Nostr event matches a given filter. Returns true or false. It is categorised as a Read tool in the Nostr Bray MCP Server, which means it retrieves data without modifying state.

How do I enforce a policy on filter? +

Register the Nostr Bray MCP server in PolicyLayer and add a rule for filter: 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 Nostr Bray. Nothing to install.

What risk level is filter? +

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

Can I rate-limit filter? +

Yes. Add a rate_limit block to the filter 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 filter completely? +

Set action: deny in the PolicyLayer policy for filter. 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 filter? +

filter is provided by the Nostr Bray MCP server (nostr-bray). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.

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