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

Annotations already establish readOnlyHint=true, openWorldHint=false, destructiveHint=false, so the safety profile is covered. The description usefully adds that results derive from natural isotope abundances and are validated against pyteomics, but says nothing about determinism, coverage limits, or how the relative abundance is normalized.

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?

A single front-loaded sentence with the core result stated first and a clarifying example in parentheses. The trailing '(validated against pyteomics)' is a minor trust signal that slightly dilutes an otherwise tight definition.

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?

An output schema exists so return values need no prose, and the description conveys what is computed. Still, for a tool sitting next to isotope_envelope it omits the one piece of context an agent most needs: when this composition tool should be chosen over the envelope tool.

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 sequence parameter ('peptide, plain one-letter residues') is already documented in the schema. The description adds the domain word 'peptide' but no format, length, or modification-handling detail beyond what the schema provides.

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 and resource: the most probable isotopic composition of a peptide plus its relative abundance, with a concrete example (how many 13C atoms). However it never distinguishes itself from the close sibling isotope_envelope, so an agent cannot confidently route between the two from this text alone.

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?

There is no when-to-use guidance, no prerequisites, and no mention of the obvious alternative isotope_envelope or peptide_mass. The agent is left to infer that this is the 'most probable composition' variant versus an envelope variant.

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