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_exc...
This record as markdown: /tools/a11y-context-mcp-server/list-patterns.md
What list_patterns does on A11y Context
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.
| Parameter | Type | Required | Description |
|---|---|---|---|
tags | array | — | |
query | string | — | |
stack | string | — | 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.
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.
Attacks that exploit this kind of access
The rule that runs list_patterns safely
PolicyLayer is an MCP gateway: it sits between your AI agents and A11y Context, and checks every tool call against a rule you set before the call runs. Nothing changes on the server itself. For list_patterns, this is the rule to start with:
list_patterns is read-only, so it stays allowed. Everything else on the server is denied unless you say otherwise.
The button opens the PolicyLayer dashboard: create your workspace, connect A11y Context, apply this rule, and every list_patterns call is checked against it from then on.
Questions about 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. It is categorised as a Read tool in the A11y Context MCP Server, which means it retrieves data without modifying state.
list_patterns accepts 3 parameters: tags, query, stack. The full parameter table on this page comes from the server's own tool schema.
Register the A11y Context MCP server in PolicyLayer and add a rule for list_patterns: 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 A11y Context. Nothing to install.
list_patterns is a Read tool with low risk. Read-only tools are generally safe to allow by default.
Yes. Add a rate_limit block to the list_patterns 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.
Set action: deny in the PolicyLayer policy for list_patterns. 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.
list_patterns is provided by the A11y Context MCP server (@a11y-context/mcp-server). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
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