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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive), so the bar is lower. The description adds genuine context beyond them: query-name normalization (RDL, press-up, lat pulldown) and the meaning of the returned muscles.main/muscles.also fields.

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-loaded with the core purpose and appropriately short. Minor waste: the opening sentence duplicates the title verbatim rather than adding information, but the remaining sentences are dense and earn their 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 single-param, read-only, no-output-schema tool, the description is nearly complete: it explains the return fields (muscles.main/also) and input tolerance. Only the absence of sibling routing keeps it from being fully self-sufficient.

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% for the single name parameter, so the baseline is 3. The description adds value beyond the schema by clarifying that colloquial/everyday names are accepted, which tells the agent it need not canonicalize input.

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 (retrieves how-to for ONE exercise) and enumerates the payload (muscles worked, picture), which distinguishes it from sibling list_exercises via the explicit singular scope. It stops short of naming the siblings to route the agent, so it's clear but not fully differentiated.

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 example queries ('how do I do a Romanian deadlift?', 'what muscles do face pulls work?') give concrete trigger conditions for when to call it. There are no explicit exclusions or named alternatives (e.g. when to prefer list_exercises), so it's clear context rather than full routing guidance.

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