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

With no annotations, the description carries the full burden of disclosing behavioral traits. It explains browser selection logic (foreground first, Chrome fallback), the return structure ({ opened, url, browser, pageId }), and the side effect of making the opened tab the current page. This is substantial context, though it omits error handling and prerequisites like device availability or browser installation.

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 concise but information-dense. Each sentence earns its place: the first states the core function, the second provides a usability comparison, the third details browser selection behavior, and the fourth explains return values and follow-up usage. It is well-structured and front-loaded with the essential purpose.

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?

Given the lack of annotations and output schema, the description covers the most critical aspects: return format, browser selection, and subsequent tool usage. It does not cover potential errors, prerequisites, or limitations, but it provides enough context for an agent to understand the tool's role and behavior. The absence of an output schema makes the explicit return description particularly valuable.

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 100% for both parameters (url and udid), so the schema already documents them well. The description does not add additional parameter-level details beyond what's in the schema, such as format expectations or edge cases. The baseline of 3 is appropriate since the schema handles parameter documentation.

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 clearly states the tool's function: 'Open a URL in a browser on an Android device.' It specifies the resource (Android browser) and the action (open a URL), and distinguishes itself from similar tools by describing its unique behavior (uses foreground browser, falls back to Chrome). This makes it distinct from siblings like android_devtools_navigate or web_navigate.

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 provides clear context for when to use the tool: to open a URL in the foreground browser, which is more direct than manual tapping. It also gives guidance on follow-up usage, stating that when pageId is non-null, subsequent android_devtools_* / webpage_* tools can be called without pageId. However, it does not explicitly name alternative tools or state when not to use it, so it lacks a full exclusionary definition.

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