Manage the database schema: read current schema, apply changes, preview changes, and audit migration history. Actions: - "get": Get the current schema (tables, columns, indexes) and api_base - "apply": Apply a declarative schema. Diffs against current and runs the safe DDL. - "dry_run": Preview t...
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AI agents use manage_schema to create or modify resources in Mcp. Write operations carry medium risk because an autonomous agent could trigger bulk unintended modifications. Rate limits prevent a single agent session from making hundreds of changes in rapid succession. Argument validation ensures the agent passes expected values.
Without a policy, an AI agent could call manage_schema repeatedly, creating or modifying resources faster than any human could review. PolicyLayer's rate limiting ensures write operations happen at a controlled pace, and argument validation catches malformed or unexpected inputs before they reach Mcp.
Write tools can modify data. A rate limit prevents runaway bulk operations from AI agents.
{
"version": "1",
"default": "deny",
"tools": {
"manage_schema": {
"limits": [
{
"counter": "manage_schema_rate",
"window": "minute",
"max": 30,
"scope": "grant"
}
]
}
}
}See the full Mcp policy for all 47 tools.
These attack patterns abuse exactly the kind of access manage_schema gives an agent. Each links to the full case and the policy that stops it:
Other write tools across the catalogue. The same approach applies to each: rate-limit and validate the arguments.
Manage the database schema: read current schema, apply changes, preview changes, and audit migration history. Actions: - "get": Get the current schema (tables, columns, indexes) and api_base - "apply": Apply a declarative schema. Diffs against current and runs the safe DDL. - "dry_run": Preview the SQL that "apply" would run, without executing - "list_migrations": List applied migrations (most recent first) Parameters by action: get: { app_id, action: "get" } apply: { app_id, action: "apply", schema, name? } dry_run: { app_id, action: "dry_run", schema } list_migrations: { app_id, action: "list_migrations" } Schema example: { tables: { posts: { columns: { id: { type: "uuid", primaryKey: true, default: "gen_random_uuid()" }, title: { type: "text", nullable: false }, author_id: { type: "uuid", references: { table: "users", column: "id", onDelete: "CASCADE" } }, created_at: { type: "timestamptz", default: "now()" } } } } } Idempotency: "apply" is safe to call multiple times. If the schema is already up-to-date, returns "Schema is up to date". Destructive operations: Require explicit opt-in via the _drop (table-level) or _dropColumns (column-level) fields. Common errors: - VALIDATION_INVALID_SCHEMA: schema format does not match the DSL - STATE_PREREQUISITE_MISSING: add _drop / _dropColumns to authorize destructive ops - QUOTA_TABLE_LIMIT: max 50 tables per app - RESOURCE_NOT_FOUND: app_id does not exist. It is categorised as a Write tool in the Mcp MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.
Register the MCP server in PolicyLayer and add a rule for manage_schema: 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 Mcp. Nothing to install.
manage_schema is a Write tool with medium risk. Write tools should be rate-limited to prevent accidental bulk modifications.
Yes. Add a rate_limit block to the manage_schema 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 manage_schema. 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.
manage_schema is provided by the MCP server (@butterbase/mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Deterministic rules across all 47 Mcp tools. Per-identity grants. Full audit log. Live in minutes. Nothing to install.
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