fuast

Roll an app back to an earlier deploy

rollback_app

DestructiveIdempotent

Makes an earlier deploy of the app live again. deploy_id comes from get_app; without it, the most recent earlier deploy that is ready. The app's data stays as it is; if that deploy's schema cannot hold the current data, nothing changes.

Tool call template

Replace each placeholder with a value matching the input schema. Only required parameters are included; add optional parameters as needed.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {
      "app": "<app>"
    },
    "name": "rollback_app"
  }
}

Input Schema

Name	Required	Description	Default
`app`	Yes	The app's slug: the first label of its address (my-app for https://my-app.fuast.com). list_apps shows the slugs you can use.
`deploy_id`	No	The deploy to make live. Default: the previous ready deploy.

Output Schema

Name	Required	Description	Default
`url`	No
`slug`	Yes
`active_deploy_id`	Yes
`previous_deploy_id`	No

Schema Changelog

Changes observed during successful MCP inspections.

First observedNov 12, 2026

TDQS

A4.4/5.0

Behavior4/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

The annotations already declare destructiveHint=true, idempotentHint=true, and readOnlyHint=false, so the safety profile is known. The description adds information the annotations cannot convey: app data survives the rollback unchanged, and the operation is effectively atomic — if the target deploy's schema cannot hold current data, nothing changes. Remaining gaps are auth/permission requirements and whether any in-flight traffic is disrupted.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness5/5

Is the description appropriately sized, front-loaded, and free of redundancy?

Three short sentences, front-loaded with the action, then the parameter source, then the side-effect contract. Every sentence carries distinct information and none repeats the schema verbatim.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness4/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

With an output schema present, return values need no explanation, and the description covers the action, the parameter source, the data-safety guarantee, and the failure mode. It could be marginally more complete by noting whether a failed precondition surfaces as an error the agent should handle or a silent no-op.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters4/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema coverage is 100%, so the baseline is 3, but the description adds provenance for deploy_id (it comes from get_app) that the schema does not state, and reinforces the default-selection rule. The app parameter's slug format is left entirely to the schema, which already documents it well.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

The description names a specific verb and resource: 'Makes an earlier deploy of the app live again.' It is unambiguously distinct from deploy_app (which creates a new deploy) and from get_app (which supplies the deploy_id), so an agent can select it without opening any schema.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines4/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

It tells the agent where deploy_id comes from ('deploy_id comes from get_app') and what happens when the parameter is omitted ('the most recent earlier deploy that is ready'), which is real routing guidance. It stops short of an explicit when-not-to-use statement or a direct comparison against deploy_app.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

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