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

The description discloses key behavioral traits beyond annotations: unrecognized columns are auto-assigned to free custom_field slots, and the mapping includes standard fields plus tenant custom fields. It does not explicitly state whether this call has side effects, and annotations (readOnlyHint=false) suggest it may not be purely read-only, but the described behavior is consistent and informative. A small gap is not clarifying if the mapping is persisted or just returned.

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 concise: three sentences, each earning its place. It front-loads the step context ('STEP 1'), then states the function, and finally provides an imperative usage note. No redundancy or unnecessary detail.

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?

Given the tool's simplicity (one param, no output schema), the description covers the essential details: purpose, usage, and a key behavior (auto-assignment). It mentions tenant-specific custom fields, adding useful context. It could be more complete by describing the return format or edge cases, but the absence of an output schema lowers the burden. Overall, it is adequately complete for an agent to select and invoke 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% with a description for 'columns' ('Exact column header names from the user's file'). The description adds value by clarifying that these are headers from a spreadsheet/CSV and by explaining how unrecognized columns are treated. This goes beyond the raw schema, helping the agent understand the parameter's role and expected behavior.

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 function: given column headers, it returns a mapping to Xmagnet fields. It also positions it as 'STEP 1 of contact upload', distinguishing it from sibling tools like upload_contacts. The verb 'returns' and specific resource ('mapping to an Xmagnet field') make the purpose unambiguous.

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?

Explicitly instructs to 'ALWAYS call this before upload_contacts' and to 'show the mapping to the user for confirmation'. This gives a clear when-to-use directive and differentiates from the alternative upload_contacts. It also implies this is a prerequisite step, providing strong usage guidance.

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