A
license-
qualityB
maintenanceEvaluates MCP servers by running read-only checks and returning a graded report with an A-F letter grade.
1
MIT
litmus
Server Details
Grade MCP servers A to F with the open behavioral litmus. npm: full toolset; hosted: lookups only.
- Status
- Healthy
- Last Tested
- Transport
- Streamable HTTP
- URL
- Repository
- polygraphso/litmus
- GitHub Stars
- 7
- Server Listing
- Polygraph
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Tool Definition Quality
A4.5/5.0
Tool DescriptionsA
Average 4.3/5 across 3 of 3 tools scored.
Server CoherenceA
Disambiguation5/5
Each tool targets a distinct operation: checking a specific server's grade, listing servers with grades, and requesting a new grade. There is no overlap or ambiguity.
Naming Consistency5/5
All tools use a consistent verb_noun pattern with underscores (check_server, list_servers, request_grade), making predictions easy.
Tool Count5/5
With only 3 well-defined tools, the set is scoped perfectly for the server's purpose—graded server lookup, listing, and grade requesting—without extraneous or missing tools.
Completeness5/5
The tools cover the full lifecycle: checking a grade, listing available grades, and requesting a new grade. No obvious gaps are present for the domain.
Available Tools
3 toolscheck_serverCheck a server's published polygraph gradeARead-onlyInspect
Read a server's published behavioral grade (A-F) from polygraph.so in under a second; no execution. The pre-flight check before recommending or installing an MCP server. On a miss it returns not_available (unevaluated: neither safe nor unsafe) with next steps.
ParametersJSON Schema
| Name | Required | Description | Default |
|---|---|---|---|
| server_ref | Yes | Registry-prefixed server ref: npm/<name>, npm/@scope/<name>, pypi/<name>, or github/<owner>/<repo>, with an optional @version. Example: npm/@modelcontextprotocol/server-filesystem |
Output Schema
ParametersJSON Schema
| Name | Required | Description |
|---|---|---|
| grade | No | A-F, present when status is graded. |
| status | Yes | Whether a published grade exists. |
| categories | No | Per-category pass/fail, present when graded. |
| report_url | No | |
| self_grade | No | One-command reproduce/grade, present on a miss. |
| server_ref | Yes | |
| version_match | No | |
| current_version | No |
Tool Definition Quality
A4.3/5.0
Behavior4/5
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare readOnlyHint and openWorldHint. The description adds concrete behavioral details: 'no execution', 'under a second', and the exact miss response format ('not_available: unevaluated'). This goes beyond the annotation hints.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.
Conciseness5/5
Is the description appropriately sized, front-loaded, and free of redundancy?
Three concise sentences with no filler. The first sentence delivers the core purpose; second gives usage context; third explains edge-case behavior. Every sentence earns its place.
Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.
Completeness5/5
Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?
Given the simple single-parameter schema, presence of output schema, and annotations, the description fully covers purpose, usage, and behavior. It is complete for an agent to select and invoke correctly without further clarification.
Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.
Parameters3/5
Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?
Schema coverage is 100% with a clear description and example for server_ref. The tool description does not add additional parameter semantics beyond what the schema provides. Baseline score of 3 is appropriate.
Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.
Purpose5/5
Does the description clearly state what the tool does and how it differs from similar tools?
The description clearly states it reads a server's published behavioral grade from polygraph.so, with a specific verb ('Read') and resource ('server's grade'). It distinguishes from siblings by positioning itself as a pre-flight check before installing an MCP server, contrasting with list_servers or request_grade.
Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.
Usage Guidelines4/5
Does the description explain when to use this tool, when not to, or what alternatives exist?
The description explicitly says 'pre-flight check before recommending or installing an MCP server', indicating when to use. It also describes the miss behavior and return value ('not_available with next steps'), but does not explicitly define when not to use or name alternatives.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
list_serversList servers with a published gradeARead-onlyInspect
Servers with a published polygraph grade, sorted A-first then by ref. Returns up to limit rows starting at offset (default limit 25, capped at 100 per call); grade restricts to one letter. summary always covers the full graded corpus (a total plus a count per grade), regardless of grade, limit, or offset.
ParametersJSON Schema
| Name | Required | Description | Default |
|---|---|---|---|
| grade | No | Restrict to servers with this grade. | |
| limit | No | Rows to return. Default 25, capped at 100 per call. | |
| offset | No | Rows to skip before taking `limit`, for paging past the first page. |
Output Schema
ParametersJSON Schema
| Name | Required | Description |
|---|---|---|
| total | Yes | Rows matching `grade` (if given), before `limit`/`offset`. Equals summary.total when grade is omitted. |
| servers | Yes | |
| summary | Yes | Always covers the full graded corpus, independent of `grade`, `limit`, or `offset`. |
Tool Definition Quality
A4.3/5.0
Behavior4/5
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations indicate readOnlyHint=true and openWorldHint=true. The description adds behavioral details beyond annotations: 'summary always covers the full graded corpus... regardless of grade, limit, or offset', which informs agents about side-effects and data scoping. No contradictions.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.
Conciseness5/5
Is the description appropriately sized, front-loaded, and free of redundancy?
Two sentences, front-loaded with the tool's purpose and sorting. Every sentence provides essential behavioral or parameter context without redundancy. Efficient and clear.
Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.
Completeness5/5
Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?
Given parameter count (3), full schema coverage, and existing output schema (not shown but noted), the description covers pagination logic, grade filtering, and summary behavior. No missing context needed for correct invocation.
Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.
Parameters4/5
Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?
Input schema covers parameters completely (100% coverage). The description adds value by explaining behavior: 'default limit 25, capped at 100 per call', 'grade restricts to one letter', and the special summary behavior. This goes beyond parameter descriptions in the schema.
Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.
Purpose5/5
Does the description clearly state what the tool does and how it differs from similar tools?
The description clearly states the tool returns 'Servers with a published polygraph grade, sorted A-first then by ref', specifying the verb (list), resource (servers), and sorting. It distinguishes from siblings check_server and request_grade which focus on individual servers or requesting grades.
Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.
Usage Guidelines3/5
Does the description explain when to use this tool, when not to, or what alternatives exist?
The description explains behavior (pagination, grade filter, summary) but does not explicitly state when to use this tool versus its siblings (e.g., when you need a full list vs. checking a single server). Usage context is implied but alternatives are not mentioned.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
request_gradeRequest a polygraph grade for an MCP serverAIdempotentInspect
Record a grade request with polygraph.so. Recording is free; only real, plausibly-MCP targets are accepted. Grading starts once the request's one-time $1 USD fee is paid: payment.payUrl is the human/browser checkout (paid in $POLYGRAPH), and payment.x402Url is the agent rail, POST the same request body there with an x402-capable client. A bare POST to x402Url returns a 402 with the exact payment requirements; retry with an X-PAYMENT header. Asset is USDC on Base mainnet (eip155:8453). On the x402 rail settlement is deferred: the authorization is charged only once a grade lands, and a run the harness cannot complete voids it, so nothing is charged. Paying starts a 48h grading clock. The fee buys the run, never the grade. After paying, poll check_server with the same server_ref for the published result, or poll statusUrl for progress.
ParametersJSON Schema
| Name | Required | Description | Default |
|---|---|---|---|
| server_ref | Yes | Registry-prefixed server ref: npm/<name>, npm/@scope/<name>, pypi/<name>, or github/<owner>/<repo>, with an optional @version. Example: npm/@modelcontextprotocol/server-filesystem |
Output Schema
ParametersJSON Schema
| Name | Required | Description |
|---|---|---|
| demand | Yes | How many times this server has been requested. |
| status | Yes | |
| created | Yes | false if the server was already recorded. |
| payment | Yes | How grading is paid for. The web checkout settles up front in $POLYGRAPH; the x402 rail takes an authorization that is charged only once a grade lands, and a run the harness cannot complete voids it, so nothing is charged. The fee buys the run, never the grade. |
| requestId | Yes | The recorded request's id. |
| statusUrl | Yes | Poll for grading progress (unpaid, grading, graded, failed); check_server also reflects the published result. |
| server_ref | Yes | The server ref that was recorded. |
Tool Definition Quality
A4.4/5.0
Behavior5/5
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations provide basic flags; description adds rich behavioral context: deferred settlement, 48h clock, fee structure, and that the fee buys the run not the grade. No contradictions.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.
Conciseness4/5
Is the description appropriately sized, front-loaded, and free of redundancy?
Single dense paragraph, front-loaded with purpose. Every sentence adds value but could be restructured for readability. Effective but not maximally concise.
Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.
Completeness5/5
Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?
Covers all necessary aspects: initiation, payment rails, polling alternatives, constraints, and outcomes. Output schema exists, so return values are not required. Fully adequate for agent use.
Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.
Parameters3/5
Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?
One parameter (server_ref) with 100% schema coverage. The description repeats the schema's description verbatim, adding no new meaning. Baseline 3 maintained.
Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.
Purpose5/5
Does the description clearly state what the tool does and how it differs from similar tools?
Clearly states 'Record a grade request with polygraph.so' using a specific verb and resource. It distinguishes from siblings (check_server, list_servers) by focusing on initiating the grade request process.
Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.
Usage Guidelines4/5
Does the description explain when to use this tool, when not to, or what alternatives exist?
Provides detailed guidance on payment and polling steps, and notes that only 'real, plausibly-MCP targets' are accepted. Lacks explicit when-not-to-use but context is sufficient.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
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