MCP Tool

One tool an MCP server advertises. Discovery creates these; an operator can also add one by hand, which is the only way to register the tools of a stdio server.

Two flags, not one

The MCP specification requires that a client treat a server's annotations as untrusted. So this model keeps what the server claimed apart from what a person decided:

• writable is set by a person and is what a consuming app should read. It defaults to True: guessing that a tool writes costs a review, and guessing the other way tells every consuming app a tool is safe when it is not. Discovery never writes this field.
• advertised_read_only mirrors the server's own readOnlyHint annotation. It is unset when the server claimed nothing. It is shown so a reviewer can see the claim, and it decides nothing.

Fields an operator owns

Field	Type	Description
enabled	boolean	Whether this tool is offered to apps reading the registry. Discovery only ever clears it, and only for a tool the server stopped advertising.
writable	boolean	Whether calling the tool changes something. Defaults to True.

Fields the discovery job owns

Field	Type	Description
mcp_server	foreign key	The server offering the tool. A tool cannot outlive it.
name	string	The tool name sent on the wire. Unique within its server, and case sensitive.
title	string	The human-readable name the server offered for display, if any.
description	text	What the tool does, as the server advertised it.
input_schema	JSON	The JSON Schema the server advertised for the tool's arguments.
output_schema	JSON	The JSON Schema the server advertised for the tool's structured result, if any.
advertised_read_only	boolean, nullable	The server's readOnlyHint claim. Unset when it claimed nothing.
definition_fingerprint	string	A digest of the title, description and both schemas. Compare it to detect that a tool's contract changed after somebody reviewed it.
last_seen_at	datetime	When discovery last saw the tool advertised. An older time means the server stopped offering it.

definition_fingerprint and last_seen_at are read-only over the REST API. enabled and writable are not: setting those over the API is a supported thing to do.

is_available

A read-only property, also exposed in the REST API. True when the tool is enabled and its server is enabled. A tool on a disabled server is not on offer however the tool itself is flagged.