URL decode

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

Annotations already declare readOnly/idempotent/closed-world, so the bar is lower. The description adds a genuinely useful behavioral fact beyond them: it errors on malformed %-sequences, which tells the agent to expect failures on invalid input.

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?

Core semantics are front-loaded in the first sentence and the error note follows logically. The trailing web-version URL is extra but harmless; otherwise there's 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?

For a small single-string transform with full schema coverage and clear annotations, the description covers purpose, mode choice, and failure behavior. Only explicit sibling routing is missing, which is a minor gap for such a simple tool.

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%, so the enum mode values and plusAsSpace flag are fully documented in the schema. The description restates mode 'full' and the '+' behavior without adding syntax or edge-case detail beyond the schema, hitting the baseline for full coverage.

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?

Names a specific verb+resource ('Decode percent-encoded text') and pins down the exact semantics by referencing decodeURIComponent/decodeURI. It's distinguishable from siblings like url_encode and url_parse by the decode verb, though it never names them explicitly.

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?

Explains the two modes and the '+' handling in passing ('form encoding'), which implies when each applies, but there's no explicit guidance on when to use this tool versus url_parse or when-not-to-use conditions.

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