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Write Support

By default, the Actian MCP Server permits only read queries. Set query_mode to read-write in conf.json to also allow Data Manipulation Language (DML) statements, that is INSERT, UPDATE, and DELETE.

Write support remains off until it is enabled. Existing read-only deployments are not affected.

Extensions can write too, through the same authorization checks described below. See Extensions.

For which tools accept a write, and how, see HCL Informix tools. The query_mode setting and the authorization checks described below apply the same way regardless of which tool performs the write.

Enabling Write Mode

Set query_mode in the conf.json file:

Value Behavior
read-only Default. Only read queries are permitted.
read-write Read queries plus INSERT, UPDATE, and DELETE are permitted. 
{
  "query_mode": "read-write"
}

Data Definition Language is always blocked

Enabling write mode does not permit Data Definition Language (DDL) or administrative statements. CREATE, ALTER, DROP, and GRANT are rejected, and so are SET, ENABLE, DISABLE, and SELECT ... INTO. This is not configurable. Use the database's native tools for schema changes.

Authorizing a Write

Writes require "query_mode": "read-write" in conf.json. In that mode, every DML statement must pass two independent checks before it reaches the database. Either one can reject it.

Check What it requires When it applies
mcp:write scope The access token must carry the mcp:write scope. Only when OAuth is enabled. A read-only server never requests or requires this scope.
Human approval A person must approve the statement in the connected client. Always, unless disabled with write_confirmation.

The scope is checked first, so a caller without it is rejected before anyone is asked to approve anything. A write counts as not approved if the person declines, does not answer before the timeout, or the client cannot display the prompt at all.

%%{init: {'theme': 'default', 'themeVariables': {'fontSize': '18px', 'fontFamily': 'arial'}}}%%
sequenceDiagram
    participant User as User
    participant Client as MCP Client
    participant Server as MCP Server
    participant DB as Database

    Client->>Server: Write request (INSERT / UPDATE / DELETE)
    Server->>Server: Check mcp:write
    alt Scope missing
        Server-->>Client: Rejected (authorization error)
    else Scope present
        Server->>Client: Request approval
        Client->>User: Show statement, table, and database
        alt User approves
            User-->>Client: Approve
            Client-->>Server: Approved
            Server->>DB: Run statement
            DB-->>Server: Rows affected
            Server-->>Client: Success
        else Not approved
            Client-->>Server: Not approved
            Server-->>Client: Rejected (write not approved)
        end
    end

The approval prompt uses the Model Context Protocol (MCP) elicitation capability, which not every client implements. If the connected client cannot display the prompt, the write is rejected, exactly as if a person had declined it. See Connecting MCP Clients for which clients support it.

To configure the mcp:write scope in the identity provider, see Auth0 or Keycloak.

Skipping the Approval Prompt

Some clients cannot display the approval prompt. For those deployments, set write_confirmation to false in conf.json to run the server's built-in write tools without asking for approval:

{
  "query_mode": "read-write",
  "write_confirmation": false
}

This removes human oversight of every write

With write_confirmation set to false, the server runs INSERT, UPDATE, and DELETE statements as soon as they are requested. Nobody is asked first. Use it only when the client cannot prompt and unattended writes by the AI agent are acceptable.

The mcp:write scope check still applies. Disabling the prompt does not grant write access to callers that lack the scope.

This setting covers the built-in write tools only. An extension that asks for approval itself always prompts, whatever this is set to. See Extensions.

The server records what it skipped. At startup it logs a warning banner stating that write confirmation is disabled, and it logs a warning for each write that ran without approval. Those entries name the tool only. They never include the statement text or the row values.

Next Steps