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

Annotations already mark it as non-read-only and non-destructive. The description adds real value beyond that: it discloses the engine (pydna) and, importantly, that output is a NEW record rather than in-place modification. It doesn't mention failure behavior when homology is insufficient or the limit constraint, so not a 5.

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 tight sentences, front-loaded with the mechanism and ending with the output behavior. No filler, every clause earns its place.

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 annotations and an output schema present, the description needn't explain returns, and the 'NEW record' note covers the key behavioral question. The main gap is absence of routing guidance to sibling assembly tools, but for correct invocation the definition is otherwise sufficient.

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 baseline is 3. The description reinforces that fragments are fused 'in order' and that features carry across, but the limit/homology and include_subject meanings are already fully documented in the schema, so little is added beyond it.

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 mechanism (overlap-extension/fusion PCR) and resource: joins fragments sharing terminal homology into one product, carrying features across, via pydna. An agent can identify the operation clearly. It doesn't explicitly contrast with adjacent joining siblings like gibson_assemble or ligate_fragments, so it falls short of 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 implied by the homology requirement ('fragments that share terminal homology'), which is a useful selection condition. However, there is no explicit when-to-use, when-not, or named alternative among the many assembly tools (gibson_assemble, ligate_fragments, golden_gate_assemble), leaving routing to inference.

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