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verdict

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Structured, sandboxed verification feedback for coding agents.

An MCP server that replaces your agent's pytest shell-outs with something built for the agent inner loop: impact-selected tests, run in an isolated environment, returning compact typed verdicts instead of 40,000 tokens of raw runner output — with failure fingerprints that tell the agent whether a failure is its regression or was broken all along.

raw pytest dump:  ~40,000 tokens, unstructured, run un-sandboxed on your machine
verdict:              ~400 tokens, typed JSON, run in a rootless container, with memory

Why

The highest-frequency tool call in agentic coding is verification — and it's the least structured. Agents re-run whole suites when one module changed, burn context parsing ANSI-coded tracebacks, run arbitrary code directly on your machine, and routinely misdiagnose pre-existing breakage as their own regression (then "fix" code that wasn't broken). verdict fixes all four.

Related MCP server: mcp-testbed

Tools

Tool

What it does

verify(scope?, base?)

Selects tests affected by your working-tree diff (static import graph via grimp), runs them via podman/docker with the worktree mounted read-only, returns typed failures with fingerprints and a preexisting flag

explain_failure(check_id)

Full traceback for one failure, on demand — bulk never rides in the summary

history(fingerprint)

First seen / last seen / times seen — regression vs. long-standing breakage

run_checks(["ruff","mypy"])

Lint and type checks, normalized into the same verdict schema

Every failure carries a fingerprint: a stable hash of the normalized failure signature (volatile tokens — addresses, tmp paths, ids, durations — collapsed). Same logical failure, same fingerprint, across runs and refactors. Fingerprints are what give verdict memory.

Quickstart

No install step needed — uvx fetches it on first use. (Or uv tool install verdict-mcp / pip install verdict-mcp for a permanent verdict-mcp command.)

Claude Code.mcp.json in your project root:

{
  "mcpServers": {
    "verdict": {
      "command": "uvx",
      "args": ["verdict-mcp"],
      "env": { "VERDICT_PROJECT": "." }
    }
  }
}

Cursor — same shape in .cursor/mcp.json.

Optional verdict.toml in your repo root:

[project]
packages = ["your_package"]          # for impact selection (auto-guessed if omitted)

[runner]
image = "ghcr.io/you/yourproj-test"  # prebuilt env with your deps
setup_cmd = "pip install -e .[test]" # or install on the fly (runs with network; tests don't)
# prefer = "local"                   # escape hatch if you have no container runtime

[limits]
max_failures = 10

Try it without an agent:

cd examples/demo_project
VERDICT_PROJECT=. verdict-mcp   # then connect any MCP client, or use the MCP inspector

Sandbox posture (v0.1)

Checks run in an ephemeral container (podman preferred, docker fallback): worktree mounted read-only at /src, copied to a writable /work inside the container, --network=none for the check run. Your host environment is never mutated by a test run. If setup_cmd is configured, that step runs with network before the check; prefer a prebuilt image for a tighter posture. No container runtime → explicit prefer = "local" fallback runs checks against a temp copy of your worktree (still never in place). See SECURITY.md for the full threat model and known limitations.

Troubleshooting: if a verdict says container engine 'podman' could not start the check, run the suggested podman pull <image> by hand — the engine's own error is the answer. One known trap on macOS: a "credsStore": "gcloud" line in ~/.docker/config.json makes podman call the gcloud credential helper for every registry, including docker.io; an expired gcloud login then breaks all pulls. Fix with gcloud auth login or remove that line.

Honest limitations

  • Impact selection uses the static import graph — approximate by design. Dynamic imports, fixture-by-name resolution, and data-driven tests can be missed; verify(scope="all") is always available and verdict says in selection_note whenever it falls back.

  • Python/pytest only today, plus ruff/mypy. The adapter interface is small and documented — vitest and go test -json adapters are the most-wanted contributions (CONTRIBUTING.md).

  • Flake detection and coverage-map-based selection are v0.2 (roadmap).

Roadmap

v0.2: coverage-based impact maps (precise selection), flake detection via fingerprint alternation, devcontainer.json support, result cache keyed on (tree hash, check, image digest). Later: vitest/jest, go test, cargo test adapters; per-repo verdict daemon mode.

License

Apache-2.0

Available Tools

4 tools
explain_failureA

Full traceback and output for one failing check from a previous verify run.

ParametersJSON Schema
NameRequiredDescriptionDefault
run_idNooptional; defaults to the most recent run containing this check.
check_idYesthe failure's check_id, e.g. 'pytest::tests/test_x.py::test_y'.

Output Schema

ParametersJSON Schema
NameRequiredDescription

No output parameters

TDQS

A4/5.0
Behavior3/5

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

With no annotations, the description carries the full disclosure burden. It reveals the return content (traceback and output) and the source (previous verify run), which is helpful. Yet it does not explicitly declare read-only behavior or lack of side effects, nor what happens if the check_id is not found. This is a moderate gap given the absence of annotation support.

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?

The description is a single, efficiently worded sentence that front-loads the core purpose and key constraint (from a previous verify run). There is zero wasted text, making it easy for an agent to parse quickly.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness4/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

Given the output schema is present and parameters are fully described, the description provides sufficient context for the tool's purpose and usage. It mentions the prerequisite of a prior verify run and the focus on a specific check. Minor omissions like error handling or explicit read-only status are not critical for basic invocation.

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 description coverage is 100%, with both run_id and check_id already documented, including the default behavior of run_id and an example for check_id. The description adds no additional semantic value beyond the schema, such as clarifying the format of output or the relationship between the parameters.

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 precisely states the tool's function: retrieving the full traceback and output for a single failing check from a prior verify run. This clearly distinguishes it from siblings like 'verify' (which runs checks) and 'history' (which lists runs), as it focuses on failure details.

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?

It provides context by specifying the tool is for a 'previous verify run', implying it should be used after a verification execution. However, it does not explicitly name alternatives or state when not to use it, leaving some room for inference about choosing it over history or re-running verify.

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

historyA

When was this failure fingerprint first/last seen, and how many times?

Use this to distinguish a regression you introduced (unknown fingerprint) from long-standing breakage (fingerprint seen across many runs/commits).

ParametersJSON Schema
NameRequiredDescriptionDefault
fingerprintYes

Output Schema

ParametersJSON Schema
NameRequiredDescription

No output parameters

TDQS

A4.2/5.0
Behavior3/5

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

With no annotations provided, the description carries the full burden of behavioral disclosure. It reveals that the tool returns historical information (first/last seen, count) and implies a read-only query, but it does not explicitly state read-only status, error handling, or any side effects. For a simple query tool, this is acceptable but not exhaustive.

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?

The description is two sentences with zero filler. The first sentence directly states the query, and the second explains the use case. It is front-loaded with the core purpose and efficiently conveys essential information.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness4/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

Given the tool's simplicity (one required parameter, output schema exists) and the description's coverage of purpose and usage, it is largely complete. It could explicitly mention that the tool is read-only, but that omission is minor given the lack of annotations and the straightforward nature of the operation.

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?

The schema defines 'fingerprint' as a plain string with no description (0% coverage). The tool description adds meaning by referring to it as a 'failure fingerprint' and using it in context, clarifying that it identifies a specific failure pattern. This compensates for the lack of schema documentation.

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 explicitly states what the tool returns (first/last seen, count) and identifies the resource (failure fingerprint). It also gives a specific use case—distinguishing new regressions from long-standing breakage—which clearly differentiates it from siblings like verify or explain_failure.

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 provides a clear when-to-use: when you need to know if a fingerprint is unknown (possible regression) or has been seen across runs/commits (long-standing breakage). It gives a concrete scenario but does not explicitly name alternatives or state when not to use the tool, so it falls just short of a 5.

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

run_checksB

Run lint/type checks ('ruff', 'mypy') in the sandbox; same verdict shape as verify.

ParametersJSON Schema
NameRequiredDescriptionDefault
checksNo

Output Schema

ParametersJSON Schema
NameRequiredDescription

No output parameters

TDQS

B3.1/5.0
Behavior2/5

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

No annotations are provided, so the description must carry the behavioral disclosure burden. It states execution is 'in the sandbox' (an environmental detail) and references the verdict shape of 'verify', but it does not disclose whether the tool is read-only, whether it modifies anything, what side effects exist (if any), or any authorization requirements. For a tool with no annotation coverage, this is a significant gap.

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?

The description is a single sentence, front-loaded with the key action, and contains zero filler. Every element ('run lint/type checks', specific tools, sandbox, shape reference) earns its place. Excellent conciseness and structure.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness2/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

While the tool is simple (one optional param, output schema present), the description leaves critical gaps: it does not explain the 'checks' parameter, relies on the reader knowing 'verify's verdict shape' (which may be defined elsewhere), and does not clarify whether all checks run or a subset can be requested. An agent may not be able to call the tool correctly without additional inference.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters1/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

The only parameter, 'checks', is entirely undocumented in the schema (0% coverage). The description mentions the tools 'ruff' and 'mypy' but never explains that 'checks' likely selects or filters which of these to run, nor does it describe the expected values. The description adds no meaning beyond the schema, leaving the parameter's role ambiguous.

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 action ('run lint/type checks') and specifies the exact tools involved ('ruff', 'mypy'), and notes the 'same verdict shape as verify' to differentiate from at least one sibling. It gives a specific, unambiguous purpose.

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 implies a context (running lint/type checks) and points to a related tool ('verify') for shape, but it does not explicitly state when to use this tool over 'verify' or the other siblings. There is no direct 'when not to use' guidance, though the intent is somewhat inferable.

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

verifyA

Verify the current working-tree changes by running affected pytest tests in a sandbox.

ParametersJSON Schema
NameRequiredDescriptionDefault
baseNogit ref to diff against (default: HEAD, i.e. uncommitted changes).
scopeNoNone for impact-based selection (default), 'all' for the full suite, or a path like 'tests/test_api.py' to run one file.

Output Schema

ParametersJSON Schema
NameRequiredDescription

No output parameters

TDQS

A3.8/5.0
Behavior3/5

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

With no annotations provided, the description carries the full burden of behavioral disclosure. It reveals that tests run 'in a sandbox', implying isolation, which is useful. However, it does not mention whether the tool modifies files, requires network access, or has any side effects on the workspace. Since it does not contradict annotations (none exist) and provides one meaningful behavioral detail, a middle score is appropriate.

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?

A single, front-loaded sentence that immediately communicates the action, target, and method. Every word contributes value, with no redundancy or filler.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness4/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

The tool is relatively simple: two optional params, no required fields, and an output schema exists (so return format need not be explained). The description covers the core behavior adequately. While it could elaborate on how 'base' and 'scope' interplay, the schema already documents those, so the description does not need to repeat them. Minor gap: it does not state whether the tool is read-only, but the sandbox hint mitigates that.

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% – both 'base' and 'scope' have descriptions in the schema. The tool description adds no additional parameter semantics beyond what the schema already provides. Per the baseline rule for high schema coverage, a score of 3 is given.

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 specific action ('Verify'), the target ('current working-tree changes'), and the method ('running affected pytest tests in a sandbox'). It distinguishes itself from siblings: explain_failure is for diagnosing failures, history is for past actions, and run_checks is a broader term that might overlap, but this tool is explicitly about pytest verification, making its niche unambiguous.

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 implies the tool is for verifying changes before committing, but it does not explicitly state when to prefer this over run_checks or provide exclusion criteria. There is no mention of alternatives or conditions that would make this tool inappropriate, leaving the routing decision to the agent's inference.

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

Tool Schema Changelog

Recent tool additions, removals, and schema changes observed during successful MCP inspections.

  1. 4 tool updatesv0.1.0
    • First observedexplain_failure
    • First observedhistory
    • First observedrun_checks
    • First observedverify

TDQS

A3.9/5.0

Scored across 4 tools

Disambiguation5/5

Each tool has a clearly distinct purpose: verify runs unit tests, run_checks runs static checks, explain_failure provides failure details, and history shows recurrence patterns. No overlap or ambiguity exists between tools.

Naming Consistency4/5

Most tools follow a verb-first convention (verify, explain_failure, run_checks), but 'history' is a noun used as a query command. The style is otherwise consistent with snake_case and lowercase, making it readable, but the mix prevents a perfect score.

Tool Count5/5

With only 4 tools, the server is tightly scoped to verification and failure analysis. Each tool earns its place, covering the necessary actions without bloat or redundancy.

Completeness5/5

The tool surface fully covers the core workflow: running tests/lint checks, explaining failures, and checking historical recurrence. There are no obvious missing operations for this domain, and the lifecycle is complete for its stated purpose.

Maintenance

ActivityMaintained
ResponsivenessResponsive

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