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

Annotations already declare this a safe read (readOnlyHint=true, destructiveHint=false), so the low bar is met, and the description adds real value beyond them: the output is an accessibility tree rather than pixels, carries element refs, and is marked with source 'web' flagged as untrusted. That untrusted-source warning is a behavioral/security trait an agent genuinely needs. What it omits is scale or truncation behavior for very large pages.

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?

One compact sentence with the resource and distinguishing characteristics front-loaded and no filler. It is a fragment rather than a full sentence, but nothing in it is redundant.

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 simple one-parameter read tool with no output schema, the description covers the essential return shape (accessibility tree with refs) and the untrusted 'web' source marking. It does not explain what a ref is or that those refs feed browser_click/browser_type, which is the core follow-on value of a snapshot 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?

There is a single parameter whose schema coverage is 100%, and the schema already explains that 'session' comes from open_app. The description adds nothing further about the session parameter, but with full schema documentation 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?

The description names the specific resource (the phone browser's page) and the exact output form (an accessibility tree with refs), which distinguishes it from the image-based browser_screenshot and the generic screen tool. The verb is only implied by the name 'snapshot', but the resource and return shape are concrete enough for an agent to identify it.

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?

There is no explicit when-to-use guidance — nothing says to prefer this over browser_screenshot or screen when the goal is to locate elements, nor any preconditions such as the browser needing to be open. The only inference an agent can make is that 'refs' are produced for targeting, which is implicit rather than stated.

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