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

Annotations already declare this a read-only, idempotent, closed-world operation, so the safety profile is covered. The description adds genuine behavioral context by describing the return shape: a capo fret, or a set of easy options when no shape key is supplied — valuable given there is no output 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 short sentences with zero filler: purpose first, input guidance second, return behavior last. No sentence is redundant with the title or schema.

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 two-parameter, read-only lookup with no output schema, the description supplies both the input expectation and the return behavior. Only a minor gap remains in not stating whether the returned easy options are ranked or formatted in a specific way.

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 would be 3, but the description goes beyond the schema by explaining the consequence of omitting shape_key (you get a range of easy options instead of a single fret) and by giving interpretive framing for both keys.

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?

The description names a specific action and resource ("works out where to put a capo") and immediately ties it to the two inputs, so an agent can distinguish it from siblings like find_key or transpose_chords without opening the 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?

It gives concrete situations for use (to match a singer or a recording) and explains the conditional case for the optional shape_key, including what happens when it is omitted. It stops short of explicitly naming which sibling tool to use instead when the agent wants an alternative approach, but the context is otherwise unambiguous.

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