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

Annotations already declare the safety profile (readOnly, non-destructive, closed-world), so the bar is lower. The description adds genuinely new behavioral context: the figure reproduces the phylogeny panel's layout exactly, and the choice of phylogram vs cladogram governs whether a scale bar appears — details not derivable from the annotations alone.

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?

Three sentences, front-loaded with the verb+resource and output format, then the panel-parity value proposition, then the input wiring instruction. No filler; every clause carries information an agent can act on.

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, return values need not be explained, and the 100%-covered parameter schema handles the 13 inputs. The description covers what the tool produces (SVG figure) and its input source, leaving only minor gaps such as whether downstream tools consume the figure directly.

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% and each of the 13 parameters is richly documented in the schema itself (layout enum rationale, branch_lengths/scale-bar coupling, min_support gating). The description only gestures at tip names, support and scale bar, adding little beyond what the schema already says, so the baseline 3 is appropriate.

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 (draw a tree as an SVG figure), then enumerates the layouts and the phylogram/cladogram distinction so the agent knows the exact output shape. It also names the sibling tools whose output feeds it (build_tree, edit_tree), separating it from neighbors like export_tree or transform_tree without needing 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?

It tells the agent where the required `newick` comes from ('Wire newick from build_tree or edit_tree') and gives a real selection rule in the unrooted case (only honest layout when no root was inferred). There is no explicit when-not guidance or contrast against sibling export/comparison tools, so it stops short of a full 5.

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