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

With no annotations, the description carries the full behavioral burden and is a mutation tool, yet it says nothing about permissions, partial-update semantics (are omitted fields left unchanged?), reversibility, or side effects on the render. It only implies a precondition (phone must already exist), which is minimal disclosure for a 37-param write operation.

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?

Three short sentences, purpose front-loaded, no filler. The middle pointer sentence and the closing routing sentence both do work, though the reference to update_screenshot is repeated in effect.

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?

A 37-parameter mutation tool with no annotations and no output schema needs far more coverage than this provides; most of the parameter surface and all behavioral semantics are unaddressed. The cross-reference to update_screenshot is the only attempt to bridge the gap.

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 only 35% across 37 parameters, so the description must compensate and largely does not. "Takes the same phone fields as update_screenshot" is a useful pointer, but it offloads meaning to another tool an agent may not have loaded and leaves most parameters (shadows, focus overlay, fades) undocumented.

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?

"Update an extra phone added with add_phone" names a specific verb (update) and resource (phone), and the third sentence distinguishes it from update_screenshot by scope (extra phone vs main phone). This differentiates it from siblings like remove_phone and set_phone_color 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?

It explicitly states the object must have been created via add_phone and routes main-phone edits to update_screenshot, giving a clear when-to-use and a named alternative. It stops short of any exclusion or condition beyond that single routing rule, so it is not a full 5.

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