Fill cells

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

Adds substantive behavior beyond the annotations: it discloses that the destination's previous contents are saved for undo_last, which confirms and deepens the destructiveHint=true signal, and it notes that formula errors found after filling are returned. These are exactly the traits an agent needs to reason about a destructive mutation.

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 behavior, then usage guidance, then the continue_series variant and side effects. Four dense sentences that mostly earn their place, though it borders on long for the amount of structured data already present.

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?

With no output schema, the description usefully reports what is returned (formula errors), covers the recoverability of the destructive write, and explains the mode/parameter behavior. Combined with full schema coverage and accurate annotations, an agent has everything needed to invoke it 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 100%, so the baseline is 3, but the description adds real semantics: it explains continue_series with concrete examples (1, 2, 3 → 4, 5, 6; Jan → Feb; dates) and clarifies relative-reference shifting that the schema only gestures at.

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 ('Fill cells from a source block') with an evocative analogy ('like dragging the fill handle or pasting onto a bigger selection') and spells out exactly what propagates: formulas with relative-reference shifting, values, and formatting. This clearly separates it from sibling tools like write_range, append_rows, or format_range.

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 a concrete when-to-use ('after writing one row or column of formulas to extend them across a table, instead of sending every column') and describes the continue_series alternative path with examples. It lacks an explicit 'when not to use' or a named sibling alternative, so it stops short of a 5.

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