h_fill

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

With no annotations, the description carries full responsibility for behavioral disclosure. It clearly states the tool operates on the editor pick rather than a selection and explains a common failure mode. However, it does not explicitly describe side effects (e.g., structure modification) or reversibility, though the operation is implied.

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 three concise sentences with no filler. The first sentence provides the core purpose, the second details usage constraints and a pitfall, and the third names the alternative tool. Every sentence earns its place.

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?

The description fully explains the tool's unique requirement (editor pick), prerequisite (atom picked in GUI), a common error, and the alternative tool for selection-based additions. Since an output schema exists, return values need not be explained. This is complete for a simple utility.

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?

The tool has zero parameters, and the schema is an empty object (100% coverage baseline is 4). The description adds valuable context by stating that it takes no selection and explaining that passing a selection would incorrectly land in the quiet argument and fail. This goes beyond the empty schema, earning a 5.

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 states the tool fills open valences on the currently picked atom with hydrogens, a specific verb+resource. It also explicitly distinguishes itself from the sibling h_add tool, which adds hydrogens to a selection.

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 explicitly states when to use this tool (requires an atom picked in the GUI, takes no selection) and directs users to h_add for selection-based additions. It also warns about passing a selection causing a specific error, preventing misuse.

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