jwt_security_testDecode JWT metadata locally to flag unsafe algorithms and claim timing without signature verification. Use it for quick JWT security checks during bug bounty testing.
Decode JWT metadata locally and flag unsafe algorithms or claim timing; does not verify a signature.
| Name | Required | Description | Default |
|---|---|---|---|
| jwt_token | Yes |
| Name | Required | Description | Default |
|---|---|---|---|
| header | Yes | ||
| payload | Yes | ||
| findings | Yes |
Changes observed during successful MCP inspections.
v2.2.0Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare readOnlyHint=true, openWorldHint=false, idempotentHint=true and destructiveHint=false, so the safety and locality profile is largely covered. The description still adds genuine value by reinforcing that decoding happens 'locally' and by disclosing the limitation that no signature verification occurs — a behavioral trait the annotations do not convey.
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 sentence carrying what it does, where it runs, what it flags, and its one hard limitation. Zero filler, correctly front-loaded.
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-value explanation is rightly omitted, and the description covers purpose plus the critical non-verification caveat for a one-parameter tool. The only shortfall is the unaddressed input format, which is minor given the simple schema.
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 description coverage is 0% for the single jwt_token parameter, so the description would need to compensate and it does not — it never states whether the expected input is a raw compact JWT, a full 'Bearer ...' header value, or a base64 segment. The parameter name is largely self-explanatory, which keeps this from scoring lower, but a real format ambiguity remains.
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 gives a concrete verb and resource ('Decode JWT metadata') plus the specific checks performed ('flag unsafe algorithms or claim timing'), and explicitly states the scope boundary ('does not verify a signature'). No sibling tool performs JWT analysis, and an agent can immediately tell what this tool produces versus the DNS/HTTP/scanning tools around it.
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 clause 'does not verify a signature' usefully rules out one misuse case, but the description never states when an agent should reach for this tool or name any alternative. Usage is implied (analyze a JWT you already have) rather than guided, which lands at the minimum-viable level.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.