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

Annotations already declare readOnly, idempotent, non-destructive, closed-world behavior, so the bar is lower; the description still adds real value by disclosing the return content (Roman numeral analysis, diatonic chord list, recommended solo scale) and by hedging with 'most likely key', signaling a heuristic rather than a definitive answer.

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?

A single front-loaded sentence: the core action comes first, then the outputs are listed in a compact parallel clause. No filler and no repetition of the title.

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?

With no output schema, the description correctly compensates by naming what comes back, which is exactly what an agent needs to decide whether this tool answers its question. Minor gap: no note on ambiguity handling or on whether an error is raised for unrecognized chord symbols.

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?

Only one parameter with 100% schema description coverage, including a concrete format example ('G D Em C'), so the schema carries the burden. The description adds nothing about chord syntax, accepted separators, or how accidentals/enharmonic spellings are handled.

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 and resource — derive the likely key of a song from a chord progression — and then enumerates the derived outputs (Roman numerals, diatonic chords, solo scale), which cleanly separates it from siblings like get_scale or transpose_chords that operate on already-known keys.

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?

Usage is only implied: the agent can infer you call this when you have a chord list and want the key, but the description never states when to prefer it over get_scale or transpose_chords, nor any exclusions. No mention of what to do with ambiguous or modal progressions.

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