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

Annotations only say readOnlyHint=false and destructiveHint=false. The description adds substantial context beyond that: it redraws the screen only if data changed, the result enumerates changed sources plus errors, a failed source retains its last good data, it fails with not_installed, and it writes a data_refresh entry to device_log.

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

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

The description is four tight sentences, front-loaded with the action and its visible effect, then covering result shape, failure semantics, and logging. Every sentence contributes information an agent needs and none repeats the schema.

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

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

There is no output schema, so the description carries the burden of explaining what comes back, which it does by describing changed sources, errors, and retained last-good data. It also covers failure behavior and audit logging, leaving nothing essential ambiguous for a two-parameter tool.

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

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

Schema description coverage is 100%, so the id and session parameters are already fully documented by the schema. The description adds no syntax or format detail beyond what the schema provides, so the baseline of 3 applies.

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

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

States a specific verb and resource ('Fetch the data of a spec app now'), scopes it to the app's HTTP data sources, and describes the visible side effect of redrawing the open screen. An agent can distinguish it from lifecycle siblings such as open_app or install_app without opening a schema.

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

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

The description implies this is the on-demand refresh path and notes that apps with a refresh interval update themselves, which hints at when to call it. However, it never explicitly says when to prefer this over waiting for the automatic interval or over which sibling to use for other app operations.

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