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

Annotations already cover the safety profile (readOnly, non-destructive, closed world), so the description wisely spends its budget on behavior instead: Needleman-Wunsch, free end gaps, IUPAC substitution matrix, and the guarantee of identical output to the trace panel. It also discloses the output form ('two gapped rows'). No failure modes or limits are mentioned, keeping it at a strong 4.

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, purpose front-loaded, then algorithm detail, then the parameter default. Every clause carries information (algorithm, gap policy, matrix, scope, default) and nothing is padding.

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, so return values need not be described, and the description still names the output form. Combined with algorithm, scope, and default-parameter behavior, an agent has everything needed to invoke this correctly on a single read.

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 all four parameters. The description's note that `reference` unset means the current record largely repeats the schema's own wording, adding little new syntax or semantic detail. 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+resource with explicit scope: 'Pairwise-align ONE sequencing read against a reference'. The 'ONE' qualifier and the pairwise framing distinguish it from the multi-sequence/alignment siblings (align_sequences, ebi_align, map_reads). The core operation is unambiguous from the first clause.

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?

Gives the downstream reason ('so the read can be graded') and the explicit default rule for `reference` when unset, plus a reproducibility rationale (same call as the trace editor). It does not name when to prefer a sibling such as align_sequences or compare_reads_to_reference, so context is clear but exclusions are absent.

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