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

Annotations already declare this is a mutation that is not destructive, so the bar is lower; the description usefully adds that timing is preserved and that only one line's text changes. It does not say what happens on an out-of-range line number or whether the updated line must be re-fetched.

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?

Two tight sentences, the mutation semantics front-loaded and the usage hint second; nothing is redundant with the name or title.

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 3-required-parameter mutation with annotations and no output schema, the definition covers what changes, what is preserved, and how lines are addressed. Missing only edge-case behavior (invalid line, response shape), which are minor here.

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 only 33% (only projectId is documented), so the description must compensate; it does by explaining that 'line' is 1-based and indexed the same way as the output of get_lyric_video, which is real meaning beyond the schema's minimum: 1. 'text' is described only as replacement text, leaving length/format limits to the schema.

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 ('Replaces the text of one lyric line'), scopes it to a single line, and distinguishes itself from the read-oriented sibling by pointing at get_lyric_video for line numbering. An agent can identify the operation without opening the schema.

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 use case ('fix misheard or misspelled words') and implicitly routes reading to get_lyric_video. It lacks explicit exclusions (e.g. what to use for re-timing or adding/removing lines), so it stops short of full when/when-not guidance.

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