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

Annotations already declare readOnlyHint=false and destructiveHint=false, so the safety profile is partly covered. The description adds the useful fact that a snapshot is returned (so the caller does not need a follow-up snapshot call), but says nothing about what happens at the start of history or whether page state is lost.

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?

Two short sentences, front-loaded with the action and followed by the return behavior. No filler; slightly terse given the sibling 'back' ambiguity, but efficient.

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 one-parameter navigation tool with no output schema, stating the action and that it returns the snapshot covers nearly everything needed to invoke it correctly. Only the edge case of no prior history is unaddressed.

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% and the single 'session' parameter already documents its origin from open_app. The description adds no meaning beyond the schema, 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 ('Go back one page in the phone browser'), which is unambiguous on its own. It does not distinguish itself from the sibling 'back' tool or explain how it relates to browser_snapshot, leaving an ambiguity an agent must resolve by name alone.

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?

Usage is implied by the name and the browser context, but there is no explicit statement of when to call this versus the generic 'back' sibling or when to prefer browser_snapshot after navigating. No exclusions or prerequisites are given.

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