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

With no annotations, the description carries the full burden and does so richly: it discloses the exact authenticatedAttributes set (contentType, messageDigest, signingTime, SMIMECapabilities), the §5.4 untag/EXPLICIT SET OF re-encoding rule, attached vs detached payload behavior, input size bounds (1B–16MB), and concrete failure modes (signing failure error code for rejected algorithms, verify-side still accepts them).

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?

The bracketed 【算法】【参数】【输出】【注意】 structure is front-loaded with purpose and scannable, and nearly every line carries information. It is dense and somewhat long, but there is little filler to cut.

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?

No output schema exists, so the description must explain returns, and it does: cms_in_hex, version, digest/signature algorithm OIDs, signer_sid, certificates_embedded, detached, and structure_tree. Combined with algorithm constraints, failure modes, and detached semantics, an agent has everything needed to invoke it correctly.

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; most parameter text is duplicated from the schema. However, the description adds one genuinely new constraint absent from the schema — the 1B–16MB input range for data_in_hex — plus the sid-locator rationale for embedding the certificate, lifting it slightly above baseline.

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 precise verb+resource: 'construct CMS SignedData signature message (RFC 5652 §5)', with the exact standard clause. An agent can distinguish this from siblings such as cms_signed_verify, cose_sign1_sign, and rsa_sign without opening any schema.

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?

The 【注意】 section gives real selection constraints: Ed25519 and SHA1 signing are rejected by the upstream builder, and RSA-PSS construction is not exposed (PSS artifacts must be verified via cms_signed_verify). This implicitly tells the agent when not to use the tool, but there is no explicit 'use this when you need a CMS structure rather than a bare signature' comparison against rsa_sign/cose_sign1_sign.

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