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

Annotations already cover the safety profile (readOnlyHint, idempotent, non-destructive, closed-world), so the description's value is in revealing the comparison dimensions returned and the zero-argument listing behavior — useful beyond the structured fields. It omits the asymmetric case (one id provided) and any indication of error behavior, which keeps it below a 5.

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?

Two sentences, no filler: the first front-loads the primary compare behavior with its output dimensions, the second immediately covers the fallback mode. The dense attribute list is functional rather than padding.

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 2-parameter, read-only tool with no output schema, the description covers both the main comparison output and the enumeration fallback, which is most of what an agent needs. The remaining gap is the partially-specified argument case and any note that ids come from this same enumeration, so a 4 rather than a 5.

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% with enums, so the baseline is 3; the description earns an extra point by defining the semantics of omitting both optional parameters, which the schema does not convey (both are optional with no stated default behavior). It does not clarify what a single-argument call does.

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 (compare) and resource (two gym exercises) and enumerates exactly which attributes are compared (muscles, equipment, spinal loading, stability, skill, loading method, plus reasons to choose each). This is distinguishable from siblings like get_exercise (single lookup) or search_exercises, and the second sentence adds a distinct enumeration mode.

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 clearly explains the no-argument mode ('Omit both to list the popular comparisons and every exercise pair id'), which is genuine when-to-use guidance. It does not name alternatives such as get_exercise or search_exercises, nor state what happens if only one exercise id is supplied, so it stops short of explicit exclusion/routing guidance.

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