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

Goes well beyond the annotations (which only say non-read-only, non-destructive, non-idempotent): it discloses the r2_key validation policy (caller-invented, foreign-tenant, and wrong-domain keys are refused) and warns that sheet_count/row_count/column_count are unverified client-reported hints because nothing server-side parses the binary. These are exactly the failure modes an agent needs to know.

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?

Three dense sentences, front-loaded with the core action and followed immediately by the key constraint and the alternative. No filler or restatement of the tool name.

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 15-parameter, no-output-schema tool it covers the critical semantics (R2 provenance, untrusted counts) and the sibling decision. It does not clarify which of the all-optional parameters are effectively required (r2_key is clearly implied but the schema marks nothing required), nor what a successful registration returns.

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 0%, so the description must carry semantic weight, and it does for the highest-risk fields: r2_key provenance/validation and the unreliability of the three count fields. However, 11 of 15 parameters (tags, source, ai_prompt, folder_id, file_size, sheet_names, analysis_summary, last_analyzed_at, deleted_at, original_filename, title) get no explanation, leaving substantial gaps.

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 ('Register a spreadsheet file row in the library') plus the crucial scope qualifier ('for bytes that already sit in R2'). It also implicitly separates itself from spreadsheet.create_with_content by naming that sibling as the tool that stores bytes and registers the row together.

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 precondition is explicit: bytes must already be in R2 and the r2_key must come from the upload route or spreadsheet.create_with_content. The closing 'NEXT' line names the alternative for the case where the bytes are not yet stored, giving the agent a clear when/when-not split.

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