# list_patterns

List the accessible UI component patterns available for a stack. Call this FIRST whenever you are about to build or modify any UI, to choose which patterns apply. Each entry has an id, summary, tags, aliases, and a selection_excerpt (its use_when / do_not_use_when bullets) — use the selection_excerpt to decide which patterns match the components in your task, then call get_pattern for each. Optionally narrow with tags or a free-text query.

Agent View of the PolicyLayer registry record for `list_patterns`. HTML page: https://policylayer.com/tools/a11y-context-mcp-server/list-patterns

## Facts

- Tool: `list_patterns`
- Server: A11y Context (`@a11y-context/mcp-server`) — https://policylayer.com/tools/a11y-context-mcp-server.md
- Install: `npx -y @a11y-context/mcp-server`
- Homepage: https://www.npmjs.com/package/@a11y-context/mcp-server
- Risk category: Read (Low risk)
- Registry record: grade A, identity unverified
- Server rate-limited: no
- Parameters: 3
- Recommended policy verdict: Allowed

## Parameters

| Parameter | Type | Required | Description |
| --- | --- | --- | --- |
| `tags` | array | no |  |
| `query` | string | no |  |
| `stack` | string | no | Target platform and framework. Defaults to 'web/react'. A stack is available only if this release bundles content for it; 'android/compose' is reserved and not |

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": "list_patterns",
    "arguments": {}
  }
}
```

## Why list_patterns is rated Low

Even though list_patterns only reads data, uncontrolled read access leaks sensitive information and racks up API costs: an agent caught in a retry loop can make thousands of calls a minute without anyone noticing.

## Use case

AI agents call list_patterns to retrieve information from A11y Context 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 A11y Context:

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

## Other tools on A11y Context (2)

- `get_foundations` — Read — https://policylayer.com/tools/a11y-context-mcp-server/get-foundations.md
- `get_pattern` — Read — https://policylayer.com/tools/a11y-context-mcp-server/get-pattern.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=a11y-context-mcp-server · API: https://policylayer.com/registry/api · Policy library: https://policylayer.com/policies/a11y-context-mcp-server