evalsmith-mcp

evalsmith answers four questions that come up every time a retriever, prompt or agent changes:

1. Is retrieval good enough? recall@k, precision@k, nDCG@k, hit rate and MRR from qrels and a ranked run.
2. Which configuration is better, and is the gap real? 2-3 configurations ranked with seeded paired-bootstrap confidence intervals.
3. Did the agent call the right tools? Trace vs. expected calls, strict or lax order, argument matchers.
4. Did the prompt change break anything? Golden-set checks on baseline vs. candidate outputs.

Everything is deterministic and runs offline. An LLM judge exists for a second opinion, but it is off by default and never decides the verdict. Results come out as a terminal table, Markdown, JSON, JUnit XML or a self-contained HTML report, and the GitHub Action turns them into a merge gate.

---

Interfaces over the same core

flowchart LR
    subgraph Clients
        A[MCP client<br/>desktop app, IDE, agent]
        B[Remote MCP client<br/>or service]
        C[Terminal / CI job]
        D[GitHub workflow]
    end
    subgraph evalsmith
        S1[MCP server<br/>stdio]
        S2[MCP server<br/>Streamable HTTP, stateless]
        S3[CLI<br/>evalsmith run]
        S4[GitHub Action<br/>uses: evalsmith-mcp@v0]
        CORE[(src/core<br/>metrics, bootstrap, matchers,<br/>checks, gates, reports)]
    end
    A --> S1 --> CORE
    B --> S2 --> CORE
    C --> S3 --> CORE
    D --> S4 --> CORE
    S3 -. exit code + JUnit + HTML .-> C
    S4 -. outputs + job summary .-> D

Interface	Entry point	Who uses it	Why it exists
MCP over stdio	dist/mcp/server.js	Desktop MCP clients, IDE assistants, local agents	An assistant can score a run, compare configs or audit a trace mid-conversation, with typed structuredContent back.
MCP over Streamable HTTP	EVALSMITH_TRANSPORT=http	Remote clients, internal platforms, the MCP Inspector	Same tools over the network. Stateless: no sessions to store, scales horizontally.
CLI / CI	evalsmith run evalsmith.yaml	Pipelines and terminals	--fail-under recall@5=0.8 turns a metric into a merge gate. Exit codes, Markdown summary, JUnit XML, HTML report.
GitHub Action	uses: diegoperezg7/evalsmith-mcp@v0	GitHub workflows	The same gates as a step, with outputs, a job summary and no install.

All four call the same functions in src/core. The MCP tools are thin adapters: parse input with Zod, call the core, return structuredContent validated against an output schema.

---

MCP surface

flowchart TB
    subgraph Tools
        T1[evaluate_retrieval]
        T2[compare_configs]
        T3[check_tool_calls]
        T4[detect_prompt_regression]
        T5[generate_report]
        T6[run_suite]
    end
    subgraph Resources
        R1["evalsmith://examples/{name}<br/>12 synthetic datasets + suite"]
    end
    subgraph Prompts
        P1[compare_rag_configs]
        P2[audit_agent_trace]
        P3[review_prompt_change]
    end
    T1 -- structuredContent --> T5
    T2 -- structuredContent --> T5
    T3 -- structuredContent --> T5
    T4 -- structuredContent --> T5
    classDef tool fill:#ffedd5,stroke:#c2410c,color:#431407
    classDef res fill:#e0f2fe,stroke:#0369a1,color:#082f49
    classDef prom fill:#ede9fe,stroke:#6d28d9,color:#2e1065
    class T1,T2,T3,T4,T5,T6 tool
    class R1 res
    class P1,P2,P3 prom

Tools

Every tool declares an input and an output Zod schema, returns structuredContent plus a JSON text block, and is annotated readOnly and non-destructive. Four tools are also idempotent and closed-world. detect_prompt_regression and run_suite are declared open-world and non-idempotent: annotations are per tool, and with the judge enabled they call an external model whose answers can vary. With the judge off (the default) they behave like the others.

Tool	Input	Output
evaluate_retrieval	qrels, run, optional k list	Mean recall/precision/nDCG/hit rate at every k, MRR, per-query values, skipped and missing queries
compare_configs	qrels, 2-3 {name, run}, primary metric, bootstrap {samples, seed, confidence}	Ranking with intervals, winner, runner-up, paired interval of the gap, significant
check_tool_calls	trace as logged (evalsmith, Anthropic Messages, OpenAI Chat or Responses), expected, order: strict | lax	passed, score, matched position and reasons per expected call, unexpected calls
detect_prompt_regression	golden, baseline, candidate, optional judge {enabled}	Verdict, pass rates, regressions, improvements, per-case failures, judge votes when enabled
generate_report	Any of the results above, gates, format: markdown | json | junit	passed, rendered report
run_suite	Optional config path to an evalsmith.yaml, gates, judge, format	passed, rendered report and every section's results, read from the suite's files

run_suite runs the same suites as evalsmith run, so a client can evaluate data that lives in files instead of pasting it into the conversation. It only reads inside the workspace root (EVALSMITH_ROOT, the directory the server started in by default), following symlinks before it checks, and runs the bundled example suite when no config is given.

Bad input (unknown metric, duplicate config names, qrels with no relevant documents) comes back as an InvalidParams tool error with a message the model can act on. A judge endpoint that is down or returns an HTTP error is an InternalError.

Resources

evalsmith://examples/{name} lists and serves the synthetic datasets in examples/datasets, so a client can try every tool before wiring in its own data:

Name	Content
rag-corpus, rag-queries, rag-qrels	20 help-center articles of a fictional invoicing app, 12 questions, graded judgements
rag-run-bm25, rag-run-hybrid, rag-run-hybrid-rerank	Top-10 rankings from three retrieval configurations
agent-trace, agent-expected	A support agent refunding a duplicate charge, and the calls it should make
prompts-golden, prompts-baseline, prompts-candidate, prompts-candidate-regressed	Six golden cases and three sets of outputs
suite	The example evalsmith.yaml

Prompts

Prompt	Argument	What it asks the model to do
compare_rag_configs	metric	Compare the configurations, report the gap with its interval and the weakest queries
audit_agent_trace	order	Check the trace and propose the smallest fix for each failed step
review_prompt_change	candidate	Detect regressions, build a Markdown report, decide ship / do not ship

A conversation with an MCP client

sequenceDiagram
    autonumber
    actor User
    participant Host as MCP client (LLM host)
    participant ES as evalsmith (stdio)
    participant Core as src/core

    User->>Host: "Is the reranker worth it on our help-center set?"
    Host->>ES: initialize, tools/list, resources/list
    ES-->>Host: 6 tools + JSON Schemas, 13 resources
    Host->>ES: resources/read evalsmith://examples/rag-qrels (+ 3 runs)
    ES-->>Host: qrels and runs as JSON
    Host->>ES: tools/call compare_configs {metric: "ndcg@5", configs: [...]}
    ES->>Core: compareConfigs(qrels, configs, "ndcg@5", {seed: 42})
    Core-->>ES: ranking, intervals, paired delta
    ES-->>Host: structuredContent {winner: "hybrid+rerank", significant: true, ...}
    Host->>ES: tools/call generate_report {format: "markdown", comparison}
    ES-->>Host: Markdown report
    Host-->>User: "Yes: +0.153 nDCG@5 over hybrid, 95% CI [0.069, 0.251]."

---

Metrics

For a query $q$ with relevant set $R_q$ (documents with grade $> 0$) and ranking $D_q$, with $D_q^{k}$ its first $k$ documents:

\mathrm{Recall@}k = \frac{|R_q \cap D_q^{k}|}{|R_q|}
\qquad
\mathrm{Precision@}k = \frac{|R_q \cap D_q^{k}|}{k}
\qquad
\mathrm{HitRate@}k = \mathbb{1}\left[\,R_q \cap D_q^{k} \neq \varnothing\,\right]

\mathrm{RR}_q = \frac{1}{\text{rank of the first relevant document}}
\qquad
\mathrm{MRR} = \frac{1}{|Q|}\sum_{q \in Q} \mathrm{RR}_q

\mathrm{DCG@}k = \sum_{i=1}^{k} \frac{\mathrm{rel}_i}{\log_2(i+1)}
\qquad
\mathrm{nDCG@}k = \frac{\mathrm{DCG@}k}{\mathrm{IDCG@}k}

$\mathrm{rel}_i$ is the graded judgement of the document at rank $i$ (linear gain, as in trec_eval), and IDCG is the DCG of the judgements sorted in descending order. Reported values are means over judged queries.

Conventions, all covered by tests:

• Queries whose judgements are all 0 are skipped and listed in skippedQueries.
• Judged queries missing from the run score 0 and are listed in missingFromRun.
• Precision divides by $k$, not by the ranking length.
• Repeated document ids in a ranking keep only their first position, as in trec_eval, so a run cannot score above 1 by repeating a relevant document.
• Cut-offs start at 1: recall@0 is rejected.

Worked example (tests/core/retrieval.test.ts): judgements a=2, b=1, c=0, ranking d, a, e, b, c. DCG@5 $= 2/\log_2 3 + 1/\log_2 5 = 1.69254$, IDCG@5 $= 2/\log_2 2 + 1/\log_2 3 = 2.63093$, so nDCG@5 $= 0.64332$; recall@3 $= 0.5$, precision@5 $= 0.4$, RR $= 0.5$.

Bootstrap. compare_configs resamples queries with replacement, using the same indices for every configuration (paired), samples times, from a seeded PRNG (mulberry32). Intervals are percentiles of the resampled means. The lead is significant when the interval of winner minus runner-up excludes zero. The same seed gives the same intervals on every machine.

Tool-call matchers

{
  "tool": "create_refund",
  "args": {
    "invoice_id": { "type": "exact", "value": "INV-2041" },
    "reason": { "type": "any" },
    "metadata": { "type": "subset", "value": { "ticket": "T-5532" } },
    "to": { "type": "regex", "pattern": "@acme-robotics\\.example$" }
  }
}

strict requires the trace to be exactly the expected calls in order; calls past the expected sequence fail the check and appear as failed test cases in JUnit. lax ignores order and pairs expected calls with trace calls by maximum bipartite matching (augmenting paths), so a loose matcher never steals the only call a stricter one accepts. Extra calls are reported without failing. Every matcher, exact included, fails when the argument is missing.

Prompt checks

exact (trimmed by default), regex, contains (case-insensitive by default), json_schema (the output is parsed and validated with Ajv) and length (min / max characters). A regression is a case that passes on the baseline and fails on the candidate. Missing outputs count as failures.

The optional judge sends both outputs to any OpenAI-compatible /chat/completions endpoint, Ollama included, at temperature 0. To cancel position bias each case is judged twice, with baseline as answer A and then as answer B. A side wins only when both orderings agree; a disagreement counts as a tie. That costs two requests per case. Its votes are reported next to the verdict.

---

Quickstart

npx -y evalsmith-mcp                       # MCP server on stdio
npm install -g evalsmith-mcp               # or install the `evalsmith` CLI and `evalsmith-mcp` server
docker build -t evalsmith-mcp . && docker run --rm -i evalsmith-mcp   # or run the server in a container

To run the bundled examples and the tests from source:

git clone https://github.com/diegoperezg7/evalsmith-mcp.git
cd evalsmith-mcp
npm ci            # also builds dist/ through the prepare script
npx playwright install chromium   # the HTML report tests open it in a real browser
npm test          # metrics, traces, MCP in-memory + HTTP, CLI exit codes, HTML report, action

node dist/cli/index.js run examples/evalsmith.yaml

Connect an MCP client (stdio)

From a terminal:

claude mcp add evalsmith -- npx -y evalsmith-mcp     # Claude Code
codex mcp add evalsmith -- npx -y evalsmith-mcp      # Codex CLI
code --add-mcp '{"name":"evalsmith","command":"npx","args":["-y","evalsmith-mcp"]}'   # VS Code

Other desktop MCP clients read an mcpServers block like this (examples/mcp-client-config.json):

{
  "mcpServers": {
    "evalsmith": {
      "command": "npx",
      "args": ["-y", "evalsmith-mcp"],
      "env": { "LOG_LEVEL": "warn" }
    }
  }
}

Restart the client, then try the compare_rag_configs prompt or ask it to read evalsmith://examples/agent-trace and check it.

Streamable HTTP

EVALSMITH_TRANSPORT=http EVALSMITH_HTTP_PORT=3333 node dist/mcp/server.js
curl -s localhost:3333/healthz                  # {"status":"ok","version":"0.1.0"}
npx @modelcontextprotocol/inspector             # connect to http://127.0.0.1:3333/mcp

Variable	Default	Purpose
EVALSMITH_TRANSPORT	stdio	stdio or http
EVALSMITH_HTTP_HOST / EVALSMITH_HTTP_PORT	127.0.0.1 / 3333	HTTP bind address
EVALSMITH_JUDGE_BASE_URL	http://localhost:11434/v1	OpenAI-compatible endpoint for the optional judge
EVALSMITH_JUDGE_MODEL	llama3.1:8b	Judge model
EVALSMITH_JUDGE_API_KEY	unset	Only for hosted endpoints
EVALSMITH_ROOT	current directory	Directory run_suite may read suites and data from
LOG_LEVEL	info	pino level; logs always go to stderr

---

CLI and CI

evalsmith run <config> [--fail-under metric=value ...] [--format table|json|markdown|html]
                       [--report file.{md,json,xml,html}] [--report-format markdown|json|junit|html]
evalsmith doctor [config] [--judge]

Gates accept recall@k, precision@k, ndcg@k, hit_rate@k, mrr, tool_calls (score of check_tool_calls) and prompt_pass_rate. Gates in the YAML file apply too; a command-line gate with the same name overrides it. A prompt regression or a failed tool-call check fails the run even without gates.

Exit code	Meaning
0	Every gate passed, no regression
1	A gate is below its threshold, the candidate regressed, or the tool calls do not match
2	Usage error, invalid config, unknown metric, unreadable dataset, judge endpoint down

Real output

node dist/cli/index.js run examples/evalsmith.yaml on the bundled datasets (examples/evalsmith.yaml):

evalsmith · ledgerly-support-assistant

Retrieval (12 queries, MRR 0.8403)
┌────┬────────┬───────────┬────────┬──────────┐
│  k │ recall │ precision │   nDCG │ hit rate │
├────┼────────┼───────────┼────────┼──────────┤
│  1 │ 0.4583 │    0.7500 │ 0.6667 │   0.7500 │
│  3 │ 0.7500 │    0.4167 │ 0.7442 │   0.9167 │
│  5 │ 0.9167 │    0.3000 │ 0.8059 │   1.0000 │
│ 10 │ 1.0000 │    0.1667 │ 0.8285 │   1.0000 │
└────┴────────┴───────────┴────────┴──────────┘

Comparison on ndcg@5 (paired bootstrap, 2000 samples, seed 42)
┌───┬───────────────┬────────┬──────────────────┐
│ # │ config        │ ndcg@5 │ 95% CI           │
├───┼───────────────┼────────┼──────────────────┤
│ 1 │ hybrid+rerank │ 0.9588 │ [0.8950, 1.0000] │
│ 2 │ hybrid        │ 0.8059 │ [0.6875, 0.9141] │
│ 3 │ bm25          │ 0.5596 │ [0.3782, 0.7354] │
└───┴───────────────┴────────┴──────────────────┘
hybrid+rerank wins on ndcg@5 (0.9588), +0.1528 over hybrid; 95% interval of the gap [0.0692, 0.2506] excludes zero.

Agent tool calls (strict)
┌──────────────────┬─────────┬────────┬───────┐
│ expected         │ matched │ status │ notes │
├──────────────────┼─────────┼────────┼───────┤
│ search_customers │ #1      │ pass   │       │
│ get_invoice      │ #2      │ pass   │       │
│ create_refund    │ #3      │ pass   │       │
│ send_email       │ #4      │ pass   │       │
└──────────────────┴─────────┴────────┴───────┘
All 4 expected call(s) matched (strict order).

Prompt regression
┌───────────────────────┬──────────┬───────────┬────────────────────┐
│ case                  │ baseline │ candidate │ candidate failures │
├───────────────────────┼──────────┼───────────┼────────────────────┤
│ classify-intent       │ pass     │ pass      │                    │
│ extract-invoice-id    │ pass     │ pass      │                    │
│ refund-policy-summary │ fail     │ pass      │                    │
│ due-date-format       │ pass     │ pass      │                    │
│ refuse-card-number    │ pass     │ pass      │                    │
│ refund-payload        │ pass     │ pass      │                    │
└───────────────────────┴──────────┴───────────┴────────────────────┘
No regressions across 6 case(s). Pass rate 83.3% -> 100.0%.

Gates
┌────────────┬────────┬────────┬────────┐
│ metric     │    min │ actual │ status │
├────────────┼────────┼────────┼────────┤
│ recall@5   │ 0.8000 │ 0.9167 │ pass   │
│ ndcg@5     │ 0.7500 │ 0.8059 │ pass   │
│ tool_calls │ 1.0000 │ 1.0000 │ pass   │
└────────────┴────────┴────────┴────────┘

PASS

Raising the bar makes the same run fail the build:

$ node dist/cli/index.js run examples/evalsmith.yaml --fail-under recall@5=0.95 --fail-under mrr=0.9 --report report.xml
...
Gates
┌────────────┬────────┬────────┬────────┐
│ metric     │    min │ actual │ status │
├────────────┼────────┼────────┼────────┤
│ recall@5   │ 0.9500 │ 0.9167 │ FAIL   │
│ ndcg@5     │ 0.7500 │ 0.8059 │ pass   │
│ tool_calls │ 1.0000 │ 1.0000 │ pass   │
│ mrr        │ 0.9000 │ 0.8403 │ FAIL   │
└────────────┴────────┴────────┴────────┘

FAIL · 2 gate(s) below threshold
Report written to report.xml
$ echo $?
1

HTML report

--report report.html (or --format html on stdout) writes the whole run to one HTML file that opens offline and follows the system light or dark mode:

• the verdict, and a card per gate with its value, threshold and status;
• retrieval metrics per k as bars with a bootstrap interval over the queries, and gate thresholds marked on them;
• the configuration comparison with each interval, the winner and the gap to the runner-up;
• expected vs. actual tool calls, with the matched pairs linked and mismatches flagged;
• baseline vs. candidate per golden case, with the failing checks one click away.

Dark mode and an opened prompt regression

Dataset text (case ids, tool names, failure messages) is embedded as JSON in a non-executable <script type="application/json"> block and rendered with textContent only. A Content-Security-Policy allows no network access and only the page's own script, by hash. Tests open a report full of markup in Chromium and check that nothing from it runs. npm run docs:screenshots regenerates the pictures above.

---

GitHub Action

- uses: actions/checkout@v5
- uses: diegoperezg7/evalsmith-mcp@v0
  id: evals
  with:
    config: evals/evalsmith.yaml
    fail-under: |
      recall@5=0.8
      ndcg@10=0.7
      tool_calls=1
    html-report: evalsmith-report.html

The step fails when a gate is below its threshold, the prompt candidate regresses or the tool calls do not match, and writes the Markdown report with the verdict to the job summary. It runs the same core as the CLI from a bundled node24 script, with no install step and no shell. examples/github-workflow.yml is a complete workflow that also keeps the HTML report as an artifact and publishes the JUnit XML as a check run.

Input	Default	Description
config	evalsmith.yaml	Suite file. Dataset paths inside it are relative to the file
fail-under		One metric=value per line. Adds to the gates in the suite file and overrides those with the same name
report-file		Report file: .md, .json, .xml (JUnit) or .html
report-format	from extension	markdown, json, junit or html
html-report		Path for the self-contained HTML report
upload-summary	true	Append the Markdown report to the job summary

Output	Description
verdict	pass or fail
failed-gates	Gates below their threshold
metrics	Retrieval metrics as JSON, e.g. fromJSON(steps.evals.outputs.metrics)['recall@5']
mrr	MRR of the retrieval run
tool-calls	Tool-call score, matched / expected
prompt-pass-rate	Candidate pass rate on the golden set
prompt-regressions	Cases that pass on baseline and fail on candidate
winner	Winning configuration of the comparison
report-file	Path of report-file, empty when not requested
html-report	Path of the HTML report, empty when not requested

Outputs of a section the suite does not have are empty. Dataset text printed to the log is wrapped in ::stop-commands::, so a case id or tool name cannot issue workflow commands. The judge reads EVALSMITH_JUDGE_* from the step environment, as the CLI does.

Without the action, the CLI does the same from any CI:

npx evalsmith run evals/evalsmith.yaml --fail-under recall@5=0.8 --format markdown --report evalsmith-report.xml >> "$GITHUB_STEP_SUMMARY"

---

Suite file

name: ledgerly-support-assistant
retrieval:
  qrels: datasets/rag/qrels.json # { queryId: { docId: grade } }
  run: datasets/rag/runs/hybrid.json # { queryId: [docId, ...] }
  k: [1, 3, 5, 10]
compare:
  metric: ndcg@5
  configs:
    - { name: bm25, run: datasets/rag/runs/bm25.json }
    - { name: hybrid, run: datasets/rag/runs/hybrid.json }
    - { name: hybrid+rerank, run: datasets/rag/runs/hybrid-rerank.json }
  bootstrap: { samples: 2000, seed: 42, confidence: 0.95 }
agent:
  trace: datasets/agent/trace.json
  expected: datasets/agent/expected.json
  order: strict
prompts:
  golden: datasets/prompts/golden.json
  baseline: datasets/prompts/baseline.json
  candidate: datasets/prompts/candidate.json
  judge: { enabled: false }
gates:
  recall@5: 0.8
  ndcg@5: 0.75
  tool_calls: 1.0

Every section is optional. Paths are relative to the YAML file.

---

Pairs with ragcompass

ragcompass profiles a corpus and recommends how to configure the RAG pipeline: parser, chunking, top-k, hybrid search, reranking. evalsmith checks whether that configuration holds up:

flowchart LR
    A[Documents] --> B[ragcompass analyze<br/>recommended configs]
    B --> C[Index 2-3 candidate configs]
    C --> D[Run the eval queries<br/>save rankings]
    D --> E[evalsmith compare_configs<br/>winner + intervals]
    E --> F[evalsmith run in CI<br/>--fail-under gates]

---

Design decisions

• Deterministic first. Metrics, matchers and checks are pure functions with hand-computed tests. A model is never needed to get a verdict, so results do not drift between runs and no paid API key is required.
• Judge off by default. When enabled it goes through any OpenAI-compatible endpoint (local Ollama works), and its votes sit next to the verdict instead of changing it.
• Intervals, not just means. Twelve queries can make a 0.03 lead look decisive. A paired bootstrap with a fixed seed makes the uncertainty visible and reproducible.
• Stateless HTTP done properly. A stateless StreamableHTTPServerTransport cannot be reused across requests, so every POST gets its own server and transport. Registration is cheap, and a test makes two consecutive calls over real HTTP to prove it.
• stdout belongs to the protocol. pino writes to stderr and ESLint forbids console in src/, so no stray byte breaks the stdio transport. The CLI keeps stdout for results only.
• One schema, three uses. The Zod schemas in src/core/schemas.ts validate MCP input, generate the JSON Schemas clients see, and type the core.

---

Project layout

src/
  core/         metrics, bootstrap, tool-call matchers, prompt checks, judge, gates, reports (incl. HTML), suite runner
  mcp/          server (stdio + HTTP), tools/, resources/, prompts/
  cli/          evalsmith run | doctor, table/json/markdown/html output
  action/       GitHub Action entry point, bundled into dist/action
  shared/       config (Zod), pino logger on stderr, MCP errors
tests/
  core/         hand-computed metrics, bootstrap, matchers, checks, reports, HTML in Chromium
  mcp/          InMemoryTransport client and real Streamable HTTP client
  cli/          exit codes 0 / 1 / 2, JUnit file, doctor
examples/
  datasets/     synthetic RAG corpus + qrels + 3 runs, agent trace, golden prompts
  evalsmith.yaml, github-workflow.yml, mcp-client-config.json

npm run check     # typecheck + eslint + prettier + vitest
npm run inspect   # MCP Inspector against the built stdio server

Releases come from version tags: release.yml publishes to npm with provenance, to the MCP Registry and to GitHub Releases, and the action is published to the Marketplace from the release. docs/RELEASING.md has the steps, including the action bundle and the v0 tag. Changes are listed in CHANGELOG.md.

License

MIT