fill_down

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

With no annotations provided, the description carries the burden. It discloses a key behavioral trait: 'Appends Table.FillDown to the table's M query,' which tells the agent the tool modifies the query. It also states the core behavior of filling nulls. However, it does not discuss edge cases such as nulls at the beginning of a column or potential side effects, leaving some behavioral uncertainty.

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 purpose, and every sentence contributes meaningful information. It is efficient and avoids redundancy, making it easy to parse.

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?

At first glance, the description covers the main action and the columns parameter format, which is adequate for a simple fill operation. However, it lacks important context such as whether it works on all partitions, how it handles nulls at the top of a column, and what the expected outcome is for the table's M query. Given the tool has 4 parameters and no output schema, a bit more detail about the transformation behavior would improve completeness.

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 schema has descriptions for columns and partitionName (50% coverage). The description adds value by specifying that 'columns is comma-separated,' which reinforces and clarifies the schema. However, it does not explain 'table' or 'sessionId', and these parameters lack schema descriptions, so the description only partially compensates for the low coverage.

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 clearly states the tool's purpose: 'replace nulls in a column with the most recent non-null value above' and mentions appending Table.FillDown. It is specific about the operation, but it does not explicitly distinguish itself from the sibling tool 'fill_up' (which likely does the opposite direction), so it misses the full sibling differentiation.

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 implies use when you want to forward-fill nulls in a Power Query column, and it mentions the comma-separated format for columns, giving some usage detail. However, it does not provide explicit guidance on when to use this tool versus alternatives like fill_up or replace_values, nor does it mention any exclusions or preconditions.

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