---
title: addressing
sidebarTitle: 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 ``<hash>_<local_name>``. 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/<hash>/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.


## Functions

### `hash_tool` <sup><a href="https://github.com/PrefectHQ/fastmcp/blob/main/src/fastmcp/server/providers/addressing.py#L29" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>

```python
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` <sup><a href="https://github.com/PrefectHQ/fastmcp/blob/main/src/fastmcp/server/providers/addressing.py#L38" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>

```python
hashed_backend_name(app_name: str, tool_name: str) -> str
```


Format the universal name for a backend tool: ``<hash>_<local_name>``.


### `parse_hashed_backend_name` <sup><a href="https://github.com/PrefectHQ/fastmcp/blob/main/src/fastmcp/server/providers/addressing.py#L43" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>

```python
parse_hashed_backend_name(name: str) -> tuple[str, str] | None
```


Parse ``<HASH_LENGTH hex>_<rest>`` → ``(hash, local_tool_name)`` or None.


### `hashed_resource_uri` <sup><a href="https://github.com/PrefectHQ/fastmcp/blob/main/src/fastmcp/server/providers/addressing.py#L55" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>

```python
hashed_resource_uri(app_name: str, tool_name: str) -> str
```


Per-tool Prefab renderer resource URI.


### `parse_hashed_resource_uri` <sup><a href="https://github.com/PrefectHQ/fastmcp/blob/main/src/fastmcp/server/providers/addressing.py#L60" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>

```python
parse_hashed_resource_uri(uri: str) -> str | None
```


Extract the hash from a Prefab renderer URI, or None.

