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

Annotations already declare readOnlyHint=false, destructiveHint=false, and openWorldHint=false, so the description needs to add domain behavior — and it adds essentially nothing beyond naming the pydna backend. It does not say that ligation frequently fails to produce product, that products are filtered to circular by default, or that end chemistry determines whether a junction forms; all of that sits in parameter descriptions rather than the tool description.

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 no filler; the em-dash clause is compact. It is arguably too short for a 12-parameter tool, but nothing in it is redundant, and the core operation leads.

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 12 parameters, nested record objects, an output schema, and several advanced traits (positional end chemistry, fill-in, partial overlaps), the description leaves the agent without guidance on input sourcing, typical failure modes, or tool selection among the many assembly siblings. The output schema removes the need to document return values, but the usage-side gaps remain substantial.

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 the parameter prose is unusually rich (positional fragment_indices, end_treatments, fill_in, end_origins), so the schema carries parameter meaning fully. The description's only parameter-adjacent content is the blunt/sticky remark, which merely restates the blunt flag; baseline 3 applies when the schema does all the work.

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 ('Ligate fragments by their overhangs') plus the molecular basis for the operation (sticky, optionally blunt) and names the underlying implementation (pydna ligation_assembly). It does not distinguish this from plausible siblings such as restriction_ligate, golden_gate_assemble, gibson_assemble, or ligation_independent_clone, so an agent cannot route between assembly tools on the strength of 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?

'sticky, optionally blunt' describes a capability, not a selection criterion. There is no statement of when to prefer this ligation over restriction_ligate or the other assembly tools, no prerequisites, and no note that inputs typically come from digest_fragments upstream (that dependency is only visible in the schema's prose).

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