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

Annotations already declare readOnly/idempotent/non-destructive, and the description adds real context beyond them: input validation behavior (mixing drop-frame with non-drop is rejected), the sign semantics of the result, and the payment model ($0.001 USDC per successful call via x402 on Solana) plus an alternate HTTPS endpoint. Cost and failure-mode disclosure is exactly what an agent needs before invoking. It stops short of saying what the error looks like when validation fails.

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?

Four short, front-loaded sentences that each carry distinct information (result semantics, format rule, validation rule), followed by the pricing/endpoint note. No filler; the only mild redundancy is the pricing line, which is nonetheless decision-relevant.

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 three-parameter, no-output-schema tool with strong annotations, the description covers what matters: sign of the result, input format constraints, rejection behavior, and cost. Remaining gaps are minor — the numeric return type and behavior when 'to' precedes 'from' at an unusual rate are not stated outright.

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%, so the description must carry parameter meaning. It does explain the critical ambiguity in 'from'/'to' — colon vs semicolon encoding and drop-frame vs non-drop consistency — but never spells out the timecode string layout (HH:MM:SS:FF) or clarifies that 'rate' means frames-per-second with the 24/25/30 values and 30 default, leaving the third parameter's meaning to the enum alone.

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 computation: number of frames between two timecodes at a shared rate. The sign convention ('positive means to is later') pins down direction. It does not name the nearby siblings (timecode_add, timecode_duration, timecode_frames), so routing relies on the reader inferring 'diff' = subtraction rather than sum/duration.

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?

Implied usage is clear from the arithmetic framing, and two preconditions are stated (both codes must share the same rate and the same colon/semicolon style; drop-frame mixing is rejected). However there is no explicit when-to-use guidance or comparison against timecode_duration or timecode_add when an agent is choosing among the timecode family.

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