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

Annotations already disclose the safety profile (destructiveHint=true, idempotentHint=true, openWorldHint=true), so the bar is lower. The description adds genuinely useful context beyond them: the old URL is replaced and recognition persists on the new URL under the same radio_id, which tells the agent the stream identity is preserved rather than recreated.

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 tight sentences: the usage constraint is front-loaded and the behavioral consequence follows. No filler, and every clause carries information the agent needs.

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 two-parameter mutation with full schema coverage, an output schema (returns needn't be described), and annotations covering mutability and idempotency, the description covers usage and effect adequately. Minor gaps remain around the fate of the previous URL and any prerequisite state, but nothing critical to correct invocation 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?

Schema description coverage is 100%, so both radio_id and url are already documented (including URL formats and twitch:/youtube: shortcuts). The description ties them together by noting the URL is replaced while radio_id is retained, but adds no syntax or format detail beyond the schema. Baseline 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 (change a stream's URL) and pins the scope to a stream the user 'already monitor[s]', which implicitly separates it from add_stream and delete_stream. The second sentence clarifies what 'change' means operationally (URL swapped, recognition continues under the same radio_id).

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 phrase 'Use this only when the user asks to change the URL of a stream they already monitor' gives a clear triggering condition and an implicit exclusion (not for creating or removing streams). It stops short of naming the alternative sibling tool (add_stream) explicitly, so it lacks the full when-not/alternative routing of a 5.

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