GD&T: Datum Feature (ISO 1101)

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

With destructiveHint=false provided by annotations, the safety profile is already clear. The description adds behavioral context about the datum's effect on gdt critique outcomes, which goes beyond annotations. However, it does not disclose what the tool returns or whether it requires existing geometry at the x,y location, leaving some behavior implicit.

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 two sentences, front-loaded with the primary action ('Place a datum feature symbol') and then the functional purpose. Every sentence earns its place, and there is no redundant repetition of the title or schema details.

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 GD&T placement tool with a complete schema and an output schema, the description provides the essential purpose and effect. It connects the tool to the broader critique workflow, which is important for agent decision-making. Minor gaps such as prerequisites (e.g., open drawing, attached geometry) and return behavior are not covered, but the overall context is adequate.

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%, so the input schema already documents all parameters. The description adds a little context by mentioning the filled triangle and boxed letter, but it does not elaborate on x, y, size, or layer beyond what the schema already provides. Baseline 3 is appropriate.

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 uses a specific verb ('Place') and resource ('datum feature symbol (filled triangle + boxed letter)'), and explains the functional consequence ('Establishes the datum so a feature control frame referencing this letter passes the `gdt` critique focus'). This clearly distinguishes it from sibling tools like gd_frame, which places the feature control frame itself.

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 clearly states the context in which the tool should be used: when a datum is needed so that a feature control frame referencing that letter will pass the gdt critique. It does not explicitly name alternatives or exclusions, but the reference to feature control frames and the critique focus gives an agent enough situational guidance.

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