---
title: prefab_synthesis
sidebarTitle: prefab_synthesis
---

# `fastmcp.server.providers.prefab_synthesis`


On-demand Prefab renderer resource synthesis.

Tools marked as Prefab (via ``app=True``, ``PrefabAppConfig``, etc.) carry
a placeholder ``meta.ui.resourceUri`` and optionally a hash in
``meta.fastmcp._tool_hash``. This module synthesizes per-tool renderer
resources on demand at ``list_resources`` and ``read_resource`` time
without storing or materializing anything.

Each tool's resource URI is ``ui://prefab/tool/<hash>/renderer.html``
where the hash comes from the tool's own meta (set at registration from
the app name + tool name). CSP on the resource is the tool's
``meta.ui.csp`` merged with the renderer defaults across all four
``*_domains`` fields.


## Functions

### `synthesize_prefab_resources` <sup><a href="https://github.com/PrefectHQ/fastmcp/blob/main/src/fastmcp/server/providers/prefab_synthesis.py#L200" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>

```python
synthesize_prefab_resources(server: FastMCP) -> list[Resource]
```


Return fresh synthetic Prefab resources for all prefab tools. Pure.


### `synthesize_prefab_resource_by_uri` <sup><a href="https://github.com/PrefectHQ/fastmcp/blob/main/src/fastmcp/server/providers/prefab_synthesis.py#L215" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>

```python
synthesize_prefab_resource_by_uri(server: FastMCP, uri: str) -> Resource | None
```


Intercept a Prefab renderer URI and synthesize on demand.


### `rewrite_tool_meta_for_wire` <sup><a href="https://github.com/PrefectHQ/fastmcp/blob/main/src/fastmcp/server/providers/prefab_synthesis.py#L228" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>

```python
rewrite_tool_meta_for_wire(tool: Tool) -> Tool
```


Return a model_copy with the per-tool URI and CSP stripped.

Reads the hash from the tool's own meta. If no hash is found,
returns the tool unchanged. Produces a fresh copy — the original
Tool object is untouched.

