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

Annotations already declare readOnlyHint=true, openWorldHint=false, and destructiveHint=false, so the safety profile is covered. The description adds genuinely useful behavior beyond that: one row per annotation and an accompanying count of distinct values per property, which is output-shaping information the annotations do not convey.

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 before the interpretive context. The closing clause about a recurring value being a group the tree does not keep together is domain framing that earns its place, though it is slightly ornate for a tool contract.

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 need not explain return values, and annotations cover safety. Given the nested _subject/_files parameters are already documented in the schema, what remains is adequate for the agent to call this correctly.

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 nexml, _files, and _subject fully, and an output schema exists. The description adds no parameter syntax or format detail beyond calling nexml a .xml tree file, so the baseline of 3 applies.

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?

The description states a specific verb and resource: read taxon annotations from a NeXML tree file, extracting every annotation on every OTU plus distinct-value counts. It clearly distinguishes the extraction purpose from structural siblings like transform_tree or compare_trees, though it never names an alternative explicitly.

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 implied rather than stated: the second sentence frames the result as tip data for the phylogeny canvas, which suggests when it is relevant. There is no explicit when/when-not guidance and no named alternative among the many tree tools (tree_statistics, compare_trees, export_tree).

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