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

Annotations already cover safety (readOnly, non-destructive, idempotent, openWorld), so the description's job is to add context — and it does exactly that: it discloses that no measurement happens in-chat or via the MCP call, preventing an agent from fabricating results, and specifies that the handoff URL must be opened on the target device. That is the single most important behavioral fact about this tool.

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, front-loaded with the disambiguating fact (no speed is measured) before the URL and the device instruction. No sentence is filler.

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 zero-parameter handoff tool with an output schema and full annotation coverage needs only to explain the handoff semantics, which the description does. Nothing an agent needs in order to call it or explain it to a user is missing.

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?

The tool takes zero parameters, so there is nothing for the description to disambiguate; baseline for a no-param tool applies. Nothing in the description conflicts with the empty 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?

States a specific verb and resource ('Opens a website speed-test handoff') and immediately negates the most likely misreading — that this call measures speed. That negation cleanly separates it from measurement siblings such as measure_latency and grade_connection_quality without needing to name them.

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?

Gives a concrete usage instruction: open the URL on the device you want to check. It implies when to use it (user wants a real speed test that this MCP cannot perform) but never explicitly names an alternative tool or a when-not condition, so it falls short of a 5.

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