> ## Documentation Index > Fetch the complete documentation index at: https://gofastmcp.com/llms.txt > Use this file to discover all available pages before exploring further. # addressing # `fastmcp.server.providers.addressing` Deterministic tool hashing for backend-tool routing and per-tool resources. Each FastMCPApp backend tool gets a deterministic hash computed from its app name + tool name. The hash serves two purposes: 1. **Backend-tool routing.** Tools with `"app"` in their visibility are callable via `_`. The dispatcher parses the prefix, then walks providers recursively (same pattern as the old `get_app_tool`) to find a tool whose stored hash matches. 2. **Per-tool Prefab renderer URIs.** Each prefab tool gets a unique renderer resource at `ui://prefab/tool//renderer.html`. `list_resources` and `read_resource` synthesize these on demand from the tool's meta. The hash is computed at registration time from `(app_name, tool_name)` — both known at that moment — and stored in `meta["fastmcp"]["tool_hash"]`. Deterministic across replicas (same code → same hash), no registry walk needed. The key is deliberately public. Keys prefixed with `_` inside the `fastmcp` meta namespace are stripped at every serialization boundary (see `FastMCPComponent.get_meta`) because they hold process-local state such as enabled/disabled marks. The hash is the opposite: a stable identity that intermediaries need in order to recognize a tool they are forwarding, so it must survive the wire. ## Functions ### `hash_tool` ```python theme={"theme":{"light":"snazzy-light","dark":"dark-plus"}} hash_tool(app_name: str, tool_name: str) -> str ``` Deterministic hex hash for a tool in an app. Same inputs on every replica produce the same output. ### `hashed_backend_name` ```python theme={"theme":{"light":"snazzy-light","dark":"dark-plus"}} hashed_backend_name(app_name: str, tool_name: str) -> str ``` Format the universal name for a backend tool: `_`. ### `parse_hashed_backend_name` ```python theme={"theme":{"light":"snazzy-light","dark":"dark-plus"}} parse_hashed_backend_name(name: str) -> tuple[str, str] | None ``` Parse `_` → `(hash, local_tool_name)` or None. ### `hashed_resource_uri` ```python theme={"theme":{"light":"snazzy-light","dark":"dark-plus"}} hashed_resource_uri(app_name: str, tool_name: str) -> str ``` Per-tool Prefab renderer resource URI. ### `parse_hashed_resource_uri` ```python theme={"theme":{"light":"snazzy-light","dark":"dark-plus"}} parse_hashed_resource_uri(uri: str) -> str | None ``` Extract the hash from a Prefab renderer URI, or None.