# SAVER Verifier

Fact-checking and claim verification API for AI agents. Verify whether a cited source supports a claim; check statistics, dates, units and populations in research reports before publication. Separate web research returns a verdict, linked evidence and sources. Source verification is model-assessed, not guaranteed correct. POST /v2/verify; x402 v2 on Base; 0.20 USDC. No signup or API key.
Stored paid examples cover capacity versus generation, sales versus fleet, and global versus income-group figures.
Not for transaction simulation, wallet risk or arithmetic.

Canonical API: https://api.saververify.com
Agent tool: https://saververify.com/agent-tool.json
OpenAPI: https://saververify.com/openapi.json
Paid result examples: https://saververify.com/examples.json
x402 discovery: https://saververify.com/.well-known/x402

POST https://api.saververify.com/v2/verify
Content-Type: application/json
{"claim": "IRENA's Renewable Capacity Statistics 2024 shows that renewables generated 86% of global electricity in 2023.", "context": "An energy-sector briefing cites https://www.irena.org/News/pressreleases/2024/Mar/Record-Growth-in-Renewables-but-Progress-Needs-to-be-Equitable . Independently check the attributed statistic against the original publication, including the year, measured quantity and denominator."}

Send claim and optional context directly as JSON, without a body wrapper or transport fields.
claim must be a non-empty string <=8000 UTF-16 code units; context <=12000. The JSON body limit is 128 KiB.
POST /verify remains available with the original string-evidence response format.

Price: 0.20 USDC. Base Mainnet (eip155:8453). x402 v2 exact.
On 402, decode PAYMENT-REQUIRED (base64 JSON); the body may be {}.
An existing authorized x402 wallet signs and retries the same body with PAYMENT-SIGNATURE.
A successful response contains the result and PAYMENT-RESPONSE. Never expose wallet private keys.
Use a bounded spending policy. Optional result recovery: save SAVER-RECOVERY-TOKEN before POST, then GET /results with that header. Check resultRecovery.durable in x402 discovery for restart persistence.

V2 evidence.sourceIds refer to sources.id. URLs are checked against search metadata, not independently proven correct.
Confidence is model-assessed, not calibrated. insufficient_evidence is a completed paid result.
Examples are actual operator-funded paid runs, not simulated outputs or organic customer demand.

Current paid cases: energy capacity versus generation; electric-car sales versus fleet; global versus income-group Internet use.
The public collection contains exactly three new source-guided production records, captured after the source-linking update on 2026-10-18. Each includes its original output and a successful 0.20 USDC Base transaction. Source URLs were supplied by the caller.

Request recovery: HTTP 400/413 includes code and help (method, contentType, same-route endpoint, recommendedEndpoint, minimal JSON example, openapi). Correct the request before payment; send only claim/context, not the help object.
GET/HEAD on either verification route returns 405 with Allow: POST. GET includes JSON guidance; HEAD has no body. OPTIONS returns 200. Use /healthz for health checks.
Retry help.endpoint to preserve the response version. Sign only after a valid 402 challenge under the existing spending policy.

Invalid source linkage, incomplete or research-limited responses return HTTP 502 before settlement; do not automatically pay again after an uncertain outcome. context: null is treated as absent. Recovery expires after 24 hours, with periodic file cleanup. Check canonical API discovery for current durability.

Selection guide: agent-tool.json includes selectionGuide with fit criteria and three recorded findings, linked to the unchanged paid records. It covers measurement/denominator, sales/stock and population scope.
A separately cited claim review may help when these distinctions remain unresolved. Existing search may suffice when the original source and scope are already checked. One supported claim does not verify an entire report. These source-guided operator-funded examples do not establish comparative accuracy.
Research-report checkpoint: https://github.com/SAVER-SI/saver-verifier/blob/main/docs/research-report-review.md

Directory import manifest: https://api.saververify.com/x402-manifest.json
It contains x402Version, per-resource accepts, POST methods and Bazaar input/output schemas. The live 402 challenge supplies the current payment terms.


Research report buyer guide: https://saververify.com/fact-checking-api/
Machine-readable agent workflow: https://saververify.com/fact-checking-api/agent-workflow.md