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

Beyond annotations (readOnlyHint=false, destructiveHint=true, idempotentHint=true), the description adds useful behavioral details: the `occurrence` parameter's 1-based selection logic, the constraint on allowed patch keys, and the return value ('updated set, or null if none'). It does not contradict annotations.

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 description is two sentences with no fluff. The first sentence front-loads the primary purpose and locators; the second packs necessary details (patch keys, occurrence behavior, return value) efficiently. Every word earns its place.

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 tool with 5 parameters and a nested object, the description covers the essential operational semantics: how to identify the set, what can be patched, how to disambiguate repeated exercises, and the return contract. Minor omissions like whether patch merges or replaces existing fields are implied by the update semantics and the presence of an output schema.

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?

With 0% schema description coverage, the description carries the burden of explaining parameters. It maps session_id, exercise_id, and set_number as locators, explicitly defines `occurrence`, and lists the allowed keys for the `patch` object. This adds meaning that the raw schema does not provide.

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 description states a clear verb ('Fix'), a specific resource ('a single set'), and the locators ('session + exercise + set_number'). It also enumerates the exact patchable fields, making it unambiguous what the tool does and how it differs from siblings like update_session.

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 description implies its usage context (correcting a set's metrics) and explains how to locate the set, but it does not explicitly mention when to prefer this tool over alternatives or call out exclusions. There is no direct guidance like 'for session-level changes, use update_session'.

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