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

Annotations already cover the safety profile (readOnly, non-destructive, openWorld), and the description adds real operational context: each call returns original and processed character counts, custom formats and compression ratios are gated to paid plans, and each call costs 1 credit. It stops short of describing failure behavior for malformed ASCII85 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?

Two compact sentences, with the core capability front-loaded and the commercial/return details trailing. The paid-plan and credit wording is slightly marketing-flavoured but each clause carries usable 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?

For a simple three-parameter, single-purpose codec with an output schema and full annotation coverage, the description supplies enough to call it correctly: modes, return contents, and plan-gated options. Only edge-case behavior for invalid payloads is absent, which is a minor gap.

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 baseline is 3; the description goes further by tying the action parameter to the encode/decode modes and by clarifying that non-standard 'format' values relate to paid-plan custom formats and compression ratios, which the schema's 'Output format' text does not convey.

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 verb and resource ('encodes text into Base85 strings or decodes existing ASCII85 payloads'), making the bidirectional codec role unambiguous. It does not explicitly contrast with near-neighbours like Base64EncoderDecoder or HTMLEntitiesEncoderDecoder, but the codec name itself is distinctive enough for selection.

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?

Both directions (encode/decode) are mentioned, which implies how to use the action parameter, but there is no explicit when-to-use guidance, no statement of when to pick this over other encoders, and no prerequisites or error conditions. Usage is inferable but not directed.

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