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

With no annotations at all, the description carries the full burden. It usefully discloses that this manipulates a simulated phone and that effects apply to the next action, which is real behavioral context. It omits key traits: whether unspecified fields persist or reset, whether repeated calls merge, and whether there are any ordering concerns.

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?

A single front-loaded sentence with a compact enumerated list and a closing timing note. Every clause carries information; nothing is wasted.

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?

For a 7-parameter nested mutation tool with no annotations and no output schema, the description does reasonable work but leaves gaps: it doesn't clarify merge-vs-replace semantics, doesn't explain the required session parameter's role (only the schema does), and says nothing about return behavior or error conditions.

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 coverage is only 14%, so the description must compensate, and it largely does: it maps to six of the seven top-level parameters (location, camera barcode, permissions, biometrics, payment, online). It adds little on nested semantics like camera.delayMs, payment.pin, biometrics.enrolled, or the enum values, but the top-level coverage is strong for a low-coverage schema.

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?

The description opens with a specific verb and resource – 'Change what the simulated phone has' – then enumerates the controllable dimensions (location, barcode, permissions, biometrics, payment, network). An agent can distinguish this from siblings like device_reset or device_log, though the description never names those alternatives explicitly.

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?

'Takes effect for the next action' is a genuinely useful usage hint about timing. However, there is no guidance on when to use this versus device_reset (which presumably clears such state), no prerequisites, and no indication of what happens to settings you don't specify.

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