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

Adds real behavior beyond the annotations: the consequence of abandonment (a held grid node blocking the next caller) and the exact outcome of a second call (the grid's 'no such session' error instead of silent success). That is useful for an agent deciding whether to confirm cleanup. Minor gap: the description asserts safety of re-calling while the annotation declares idempotentHint=true, and it never states whether the session can be recreated or what permissions are required; not an outright contradiction, but the two statements should be read together.

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 sentences, each carrying distinct load: what it does, which identifier to pass, when to call it and why, and what happens on a repeat call. The purpose and the identifier rule are front-loaded with no 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?

One required parameter, no output schema, and annotations already covering the safety profile — so the remaining burden is guidance and side-effect disclosure, both of which the description supplies (grid-node blocking, double-call error). Nothing an agent needs to invoke this correctly 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 coverage is 100%, so the baseline is 3, but the description earns extra credit by disambiguating the parameter against a plausible confusion: 'Takes the sessionId, not a udid.' That prevents a real mis-invocation that the schema alone would not flag.

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 ('End') and resource ('a session created by session_create'), and immediately ties it to the sibling that produces the resource. An agent can distinguish it from session_list, session_get_title, or ios_end_session without opening the schema.

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 an explicit directive with the reason: 'Always call it when finished — an abandoned session keeps its grid node until the grid times it out, which blocks the next caller.' That is when-to-use plus the cost of not using it, which is stronger than most sibling definitions in this set.

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