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

With no annotations, the description carries the burden and does disclose two important traits: the operation is confirm-gated (preview vs execute) and exercises input is destructive/replacing rather than additive. It does not cover permission requirements or what the preview/response contains, so it stops short of full transparency.

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?

Front-loads the core action and the planId requirement in the first two sentences, then spends the remaining text only on the highest-risk details (list replacement, exercise shape, day values). No filler or repetition of schema-obvious facts.

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 an 8-parameter mutation tool with no annotations and no output schema, the description supplies the critical behavioral and replacement semantics an agent needs. It leaves the date/description fields unexplained and the confirm flow's return behavior to the schema, but nothing essential 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 coverage is only 25%, so the description must compensate and does: it explains exercises REPLACES the full list, gives the exercise item shape and points to create_workout_plan for the canonical fields, and supplies the [MONDAY..SUNDAY] value set for days that the schema lacks. It is silent on startDate/endDate/title/description semantics, leaving a residual gap.

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+resource ('Edit an existing workout plan') and immediately distinguishes itself from create_workout_plan (partial field update) and swap_workout_exercise (single-slot change). An agent can pick this tool over its near-namesake siblings 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?

Gives explicit invocation guidance ('Pass planId plus only the fields to change'), an explicit alternative with its selecting condition ('to change a single slot use swap_workout_exercise instead'), and the full-list replacement rule for exercises. The when/when-not split is spelled out rather than implied.

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