ass_update_line

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

With no annotations supplied, the description carries the full burden and does well: it discloses that unspecified fields are left unchanged, that the change is reversible via ass_undo, and the index encoding convention. It stops short of stating permission requirements, whether the document must be selected, or alternative time-format edge cases.

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?

Front-loads the core partial-update semantics, then groups the remaining notes into short, scannable fragments. The return-shape sentence is somewhat redundant given an output schema exists, but it is compact and not padded.

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 13-parameter mutation tool with no annotations, the description covers the critical surprises (partial update, 0-based index, format flexibility, undoability). An output schema exists so the return-value restatement is unnecessary, and the unresolved doc_id/context behavior leaves a minor gap overall.

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 0% across 13 parameters, so the description must compensate. It adds meaning for index (0-based), start_ms/end_ms (milliseconds or time strings), and comment (Comment:/Dialogue: toggle), but leaves doc_id, layer, style, actor, effect, and the three margins entirely to the raw schema.

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?

States a specific verb and resource ("Change individual fields of one line") and clarifies the partial-update semantics with "only the fields you pass change", which separates it in spirit from the plural sibling ass_update_lines. It never names that sibling explicitly, so an agent must infer the single-line vs multi-line distinction.

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?

Gives concrete usage conditions: fields are optional and only supplied ones mutate, index is 0-based, comment=True/False toggles line type, and the operation is snapshot-backed so ass_undo reverts it. No explicit when-not-to-use or routing to ass_update_lines/direct alternatives, but the context is clear.

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