add_hairpin

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

With no annotations, the description carries the full burden, and it does disclose a genuinely non-obvious side effect: a hairpin starting at a dynamic joins that dynamic's group and is reported as merged_into. It also states the return content (direction, positions, drawn length), which compensates for the absent output schema. It stops short of covering failure conditions, permission requirements, or whether the created hairpin is reversible.

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?

The core action is front-loaded, followed by the kind list, a concrete coordinate example, the voices note, the merge caveat, and the return value — each clause adds information. The prose is dense but not padded; a slight cost is that five distinct points are packed into one paragraph.

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 10-parameter mutation tool with no annotations and no output schema, the description covers more than most: return contents, merge behavior, multi-voice usage. It remains incomplete on positioning syntax (pos/to_pos) and on flow and voice semantics, which an agent needs to call the tool correctly.

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 0% across 10 parameters, so the description must compensate, and it only partly does: 'bar 33 beat 0 to bar 33 beat 3/2' implicitly maps bar/beat and to_bar/to_beat, and voices is explained well. The string-typed pos/to_pos format, the singular voice, and the flow parameter are never given meaning anywhere.

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 the resource and its concrete kinds (cresc, dim, messa_di_voce) and states it spans from one position to another, so an agent knows exactly what is created. It does not explicitly contrast itself with near neighbours like add_dynamic or add_span, so sibling differentiation is left to inference.

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 a placement rule ('wherever notes start (also inside a held note)') and explains when to use the voices parameter ('same hairpin on several instruments ... whole string section'). There is no explicit when-not guidance or named alternative tool, so usage is implied rather than directed.

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