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

Annotations already declare readOnlyHint, idempotentHint and openWorldHint, so the safety profile is covered. The description adds real value beyond that by clarifying what the check deliberately does NOT do (no registry lookup, no account verification), which prevents the agent from over-trusting the result.

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 what it does and then the scope boundary. Every clause earns its place with no filler.

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 explained, and annotations carry the safety profile. For a single-parameter format validator the description supplies exactly the missing context: the scope boundary and validation rule.

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 coverage is 100% for the single 'ifsc' parameter, so the schema already documents it; baseline is 3. The description adds a small amount of semantic detail by noting the fifth-character-zero rule, which is param-relevant, but it does not describe accepted value shapes beyond what the schema provides.

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 (Check) and resource (the 11-character Indian IFSC format), and immediately bounds the scope by naming the detail it validates (the fifth-character zero). The negative clause 'No bank-branch registry lookup or account verification' clearly separates it from richer verification tools in the sibling set.

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 gives explicit when-not guidance ('No bank-branch registry lookup or account verification'), telling the agent this is pure syntactic validation rather than a lookup. It does not name a specific sibling alternative, so it falls short of a full 5, but the exclusions are unambiguous.

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