# hash_exists

Check if field exists in hash. Args: key: The name of the key field: The field name Returns: Boolean result or error message

Agent View of the PolicyLayer registry record for `hash_exists`. HTML page: https://policylayer.com/tools/aws/hash-exists

## Facts

- Tool: `hash_exists`
- Server: AWS (`@awslabs/mcp`) — https://policylayer.com/tools/aws.md
- Install: `npx -y @awslabs/mcp`
- Homepage: https://github.com/awslabs/mcp
- Risk category: Read (Low risk)
- Registry record: grade F, identity verified
- Server rate-limited: no
- Parameters: 0
- Recommended policy verdict: Allowed

## Example call (MCP tools/call, JSON-RPC 2.0)

```json
{
  "jsonrpc": "2.0",
  "id": 1,
  "method": "tools/call",
  "params": {
    "name": "hash_exists",
    "arguments": {}
  }
}
```

## Why hash_exists is rated Low

This tool performs a simple existence check on a hash field, which is a read-only operation with no side effects. It queries state but does not create, modify, delete, or execute any operations. The blast radius of misuse is minimal—an agent could only learn whether a field exists in a hash structure.

From the tool's own definition: "Tool description states 'Check if field exists in hash' with return type 'Boolean result or error message'. This is a query operation that retrieves existence information without modifying data."

## Use case

AI agents call hash_exists to retrieve information from AWS 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 AWS:

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

## Other tools on AWS (299)

- `bulk_delete_by_criteria` — Destructive — https://policylayer.com/tools/aws/bulk-delete-by-criteria.md
- `cache_delete` — Destructive — https://policylayer.com/tools/aws/cache-delete.md
- `cache_delete_many` — Destructive — https://policylayer.com/tools/aws/cache-delete-many.md
- `cache_delete_multi` — Destructive — https://policylayer.com/tools/aws/cache-delete-multi.md
- `cache_flush_all` — Destructive — https://policylayer.com/tools/aws/cache-flush-all.md
- `delete` — Destructive — https://policylayer.com/tools/aws/delete.md
- `delete_access_key` — Destructive — https://policylayer.com/tools/aws/delete-access-key.md
- `delete_datastore` — Destructive — https://policylayer.com/tools/aws/delete-datastore.md
- `delete_group` — Destructive — https://policylayer.com/tools/aws/delete-group.md
- `delete_image_set` — Destructive — https://policylayer.com/tools/aws/delete-image-set.md
- `delete_instance_in_series` — Destructive — https://policylayer.com/tools/aws/delete-instance-in-series.md
- `delete_instance_in_study` — Destructive — https://policylayer.com/tools/aws/delete-instance-in-study.md
- `delete_patient_studies` — Destructive — https://policylayer.com/tools/aws/delete-patient-studies.md
- `delete_resource` — Destructive — https://policylayer.com/tools/aws/delete-resource.md
- `delete_role_policy` — Destructive — https://policylayer.com/tools/aws/delete-role-policy.md
- `delete_series_by_uid` — Destructive — https://policylayer.com/tools/aws/delete-series-by-uid.md
- `delete_study` — Destructive — https://policylayer.com/tools/aws/delete-study.md
- `delete_user` — Destructive — https://policylayer.com/tools/aws/delete-user.md
- `delete_user_policy` — Destructive — https://policylayer.com/tools/aws/delete-user-policy.md
- `detach_user_policy` — Destructive — https://policylayer.com/tools/aws/detach-user-policy.md
- `json_arrtrim` — Destructive — https://policylayer.com/tools/aws/json-arrtrim.md
- `json_clear` — Destructive — https://policylayer.com/tools/aws/json-clear.md
- `json_del` — Destructive — https://policylayer.com/tools/aws/json-del.md
- `list_pop_left` — Destructive — https://policylayer.com/tools/aws/list-pop-left.md
- `list_trim` — Destructive — https://policylayer.com/tools/aws/list-trim.md
- `remove_instance_from_image_set` — Destructive — https://policylayer.com/tools/aws/remove-instance-from-image-set.md
- `remove_series_from_image_set` — Destructive — https://policylayer.com/tools/aws/remove-series-from-image-set.md
- `set_pop` — Destructive — https://policylayer.com/tools/aws/set-pop.md
- `sorted_set_remove_by_lex` — Destructive — https://policylayer.com/tools/aws/sorted-set-remove-by-lex.md
- `sorted_set_remove_by_score` — Destructive — https://policylayer.com/tools/aws/sorted-set-remove-by-score.md
- …and 269 more: https://policylayer.com/tools/aws.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`

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Source: the PolicyLayer MCP registry — one continuously verified record per MCP server. Full record: https://policylayer.com/registry?q=aws · API: https://policylayer.com/registry/api · Policy library: https://policylayer.com/policies/aws