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

Annotations already cover read-only, idempotent, non-destructive, closed-world behavior, yet the description still adds substance: the output range 'frets 0 to 9', that it returns shapes and easy open chord counts, and the clarification that ease counts chord names rather than fingerings. That output-shape context goes beyond the annotations and schema.

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?

Three tight sentences: trigger first, then output and input constraints, then exclusions and a caveat. No filler, and the most decision-relevant information is front-loaded.

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?

Even though an output schema exists, the description still tells the agent what kind of results to expect and the input cardinality limits. For a two-optional-parameter, no-required-input tool, nothing needed to invoke it correctly 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 100%, so the baseline is 3; the description earns one more by restating the key-vs-chords exclusivity as an operational rule and clarifying that the ease metric applies to chord names, which shapes how an agent should build the chords array. The 1-100 / 80-character limits merely repeat the schema.

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?

Opens with a specific verb and resource: 'capo chart or capo calculator for a sounding key or chord list', which is concrete and distinct from chord-sheet or transposition work. It never names the sibling tools, so differentiation is by domain inference rather than explicit contrast.

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?

'Use this when you want a capo chart or capo calculator' gives a clear triggering condition, and 'Does not process audio, tablature or staff notation' sets a negative boundary. It stops short of naming show_chord_sheet or transpose_chords as the alternatives to pick instead.

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