Chapters

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

Annotations declare destructiveHint=true and readOnlyHint=false, and the description usefully clarifies the operation writes into a *copy* without re-encoding, so the source video is not mutated, and that default output lands under SCREENCAST_HOME/edits. It still does not mention that an existing output requires the overwrite flag or what happens on failure, but the annotations plus the copy semantics cover the main risk.

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 sentences, front-loaded with the core action, and the parenthetical enumerates sources compactly. The trailing subtitle sentence is slightly bolted-on but each sentence carries information an agent needs.

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?

With an output schema present the description needn't explain returns, and the no-re-encoding/copy detail is valuable for a destructive tool. However, with zero required parameters across 11 options there are meaningful input combinations (input vs sessionId, transcript required for from:transcript) that the description does not disambiguate, leaving gaps the schema alone must close.

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 100%, so the schema already documents every parameter including the `from` enum and default minChapterSec values. The description restates the source options ('markers, scene changes, transcript, or a list') and subtitle muxing, adding confirmation but no format or default detail beyond the schema — the baseline 3 for full schema 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?

States a specific verb (write) and resource (chapters) plus the accepted sources and the fact it operates on an mp4/mkv/mov copy without re-encoding. It also flags two side capabilities (YouTube text output, soft-subtitle mux) that separate it from plain subtitle tools, though it never names a sibling such as burn_subtitles.

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?

Usage is only implied through the enumerated chapter sources (markers, scenes, transcript, explicit list); there is no explicit 'use this when...' statement and no exclusion of alternatives. The natural alternative, burn_subtitles for hard-burned subs versus this tool's soft mux, is never distinguished, leaving the agent to infer the routing.

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