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

Annotations already declare this is a non-destructive, closed-world (in-silico) operation, so the safety profile is covered. The description adds the meaningful behavioural note that features are propagated onto the product, but says nothing about failure when homologues are too short (the limit parameter governs this) or what happens to fragment order.

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 compact sentence, front-loaded with the method name and action with no filler. Every clause (join fragments, terminal homology, feature carry-over, pydna provenance) contributes information.

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 and the annotations plus fully documented nested schema carry most of the burden, so the description needs only to establish what the tool computes, which it does. Minor gaps remain around default inclusion of the subject as the first fragment and minimum-homology failure behaviour, though both are covered by schema defaults.

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 all five parameters, including limit, fragments ordering, and include_subject, are already explained in the schema. The description adds no parameter-level detail beyond the general idea of shared terminal homology, so the baseline 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 names a specific method ('Overlap-extension (fusion) PCR'), the concrete action ('join fragments that share terminal homology into one product'), and an extra effect ('carrying their features across'), so an agent knows exactly what it produces. It does not explicitly distinguish itself from the near-neighbour siblings (gibson_assemble, ligate_fragments, pcr_amplify), which keeps it below a 5.

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: 'fragments that share terminal homology' signals the precondition for calling it, but there is no explicit when-to-use vs. when-to-prefer-an-alternative guidance despite several assembly siblings existing. No prerequisites about fragment ordering or input sources are stated in the description.

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