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

Annotations only cover the safety profile (readOnly=false, idempotent=false, destructive=false); the description goes far beyond by disclosing the exact return payload, the powerScore threshold semantics ('50+ average = high energy impact'), thermal sampling cadence, that frames are DEVICE-WIDE not per-app, that baselines require 60 s+ recordings, and that battery drain is deliberately not measured.

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?

The purpose is front-loaded in the first clause and the remaining text is dense but earns its place because no output schema exists to document the return shape. It is a single unbroken block with no grouping or bullets, which hurts scannability for a payload this complex.

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?

With no output schema, the description carries the entire burden of documenting the response, and it does so thoroughly: time-series, per-process summary, derived leak/spike facts, energy impact, thermal block, baseline, and frames. Nothing an agent needs to interpret the result 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?

There is a single required parameter with 100% schema description coverage, so the schema already documents it fully. The description adds no format or constraint detail beyond what the schema states, which matches the baseline-3 rule for high coverage.

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 opening clause states a specific verb and resource ('Stop a performance recording') and names the sibling that must precede it ('started with ios_performance_record_start'), letting an agent distinguish it from the start tool without opening a 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?

It gives an explicit prerequisite (a recording started via ios_performance_record_start), which is clear usage context. It does not, however, route the agent between this and alternatives such as ios_performance_snapshot or android_performance_record_stop, so no exclusions are offered.

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