Format D2 Code

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

Annotations already declare readOnlyHint, idempotentHint, and non-destructive behavior. The description adds valuable context beyond those hints: it normalizes formatting, preserves semantic meaning, requires the d2 binary, and fails if the binary is missing or syntax is invalid. This is consistent with the annotations and gives the agent realistic expectations.

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 description is well organized with clear sections: purpose, behavior, binary requirement, args, returns, examples, and error handling. Every section contributes useful information and there is no filler. The most important scoping detail (requiring the d2 binary) is front-loaded early.

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 tool with one simple parameter, no output schema, and rich annotations, the description fully covers the calling context: what it does, what it returns, when it fails, and how it differs from siblings. Nothing an agent needs 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 description coverage is 100% and the single parameter d2_code is already well described in the schema. The description's Args section repeats the same meaning without adding constraints like minLength or maxLength. Baseline 3 is appropriate because the schema carries the parameter documentation burden.

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 opens with a specific verb and resource: 'Format D2 diagram source code using the d2 binary formatter.' It goes on to state the canonicalization goal and semantic equivalence, and it explicitly contrasts with d2_render and d2_validate regarding the WASM vs binary backend, which differentiates it from siblings.

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 provides clear context for when to use the tool ('Clean up', 'Normalize after editing') and explicitly distinguishes it from siblings by noting the d2 binary requirement, saying 'unlike d2_render and d2_validate which use WASM.' It does not explicitly say 'use d2_validate for validation' but the context is sufficient.

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