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

Annotations already declare readOnlyHint=true and openWorldHint=true, so safety and network access are covered; the description adds real value by disclosing that SSTV output is PNG and that the watermark layer depends on the original seed. However, with no output schema, it never says how the non-image layers are returned or what the default 'all layers' behavior does when `layers` is omitted.

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?

A single front-loaded sentence led by the verb and resource, with the layer inventory and the two critical caveats in compact parentheticals. Every clause carries information; nothing is padded.

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 no-output-schema, open-world decoding tool with one undocumented schema parameter, the description covers inputs and layer meaning but leaves the return shape (non-image layers) and the cost/latency of decoding every layer unstated. An agent can call it, but cannot predict the response structure.

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 only 33% – `seed` has no description and `layers` items carry no per-value docs – and the description compensates by explaining that seed is 'the seed used to render' for the watermark and by mapping each layer name to its meaning (spectral glyph, prime count, modem text). It still does not state what happens when `layers` is omitted versus passed.

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?

Specific verb (Decode) plus the exact resource (Delta Signal layers from a WAV/MP3/M4A file) and an enumeration of the layers produced: heartbeat, glyph, primes, watermark, ggwave, modem, SSTV. An agent can immediately separate this from the sibling tools (describe_engine, preview_card, render_signature, verify_signature), which are all signature/card oriented.

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?

States the input precondition clearly (https URL, WAV/MP3/M4A only, 'convert other formats first') and notes the watermark layer requires the render seed, which tells the agent when this tool is callable and when a prerequisite is missing. It stops short of naming an alternative tool or an explicit 'do not use this for X' case.

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