"be on to" meaning in English

{
  "forms": [
    {
      "form": "is on to",
      "tags": [
        "present",
        "singular",
        "third-person"
      ]
    },
    {
      "form": "being on to",
      "tags": [
        "participle",
        "present"
      ]
    },
    {
      "form": "was on to",
      "tags": [
        "past"
      ]
    },
    {
      "form": "been on to",
      "tags": [
        "participle",
        "past"
      ]
    }
  ],
  "head_templates": [
    {
      "args": {
        "1": "be<is,being,was,been> on to"
      },
      "expansion": "be on to (third-person singular simple present is on to, present participle being on to, simple past was on to, past participle been on to)",
      "name": "en-verb"
    }
  ],
  "lang": "English",
  "lang_code": "en",
  "pos": "verb",
  "senses": [
    {
      "categories": [
        {
          "kind": "other",
          "name": "English entries with incorrect language header",
          "parents": [
            "Entries with incorrect language header",
            "Entry maintenance"
          ],
          "source": "w"
        },
        {
          "kind": "other",
          "name": "English phrasal verbs formed with \"on\"",
          "parents": [],
          "source": "w"
        },
        {
          "kind": "other",
          "name": "English phrasal verbs formed with \"to\"",
          "parents": [],
          "source": "w"
        },
        {
          "kind": "other",
          "name": "Pages with 1 entry",
          "parents": [],
          "source": "w"
        },
        {
          "kind": "other",
          "name": "Pages with entries",
          "parents": [],
          "source": "w"
        }
      ],
      "examples": [
        {
          "text": "I was planning it as a surprise, but I think he is on to me.",
          "type": "example"
        }
      ],
      "glosses": [
        "To figure out; to realize the truth."
      ],
      "id": "en-be_on_to-en-verb-BYdE7sY8",
      "links": [
        [
          "figure",
          "figure"
        ]
      ],
      "raw_glosses": [
        "(idiomatic) To figure out; to realize the truth."
      ],
      "related": [
        {
          "word": "catch on to"
        },
        {
          "word": "cotton on to"
        }
      ],
      "tags": [
        "idiomatic"
      ]
    }
  ],
  "sounds": [
    {
      "audio": "en-au-be on to.ogg",
      "mp3_url": "https://upload.wikimedia.org/wikipedia/commons/transcoded/a/a9/En-au-be_on_to.ogg/En-au-be_on_to.ogg.mp3",
      "ogg_url": "https://upload.wikimedia.org/wikipedia/commons/a/a9/En-au-be_on_to.ogg"
    }
  ],
  "word": "be on to"
}

{
  "forms": [
    {
      "form": "is on to",
      "tags": [
        "present",
        "singular",
        "third-person"
      ]
    },
    {
      "form": "being on to",
      "tags": [
        "participle",
        "present"
      ]
    },
    {
      "form": "was on to",
      "tags": [
        "past"
      ]
    },
    {
      "form": "been on to",
      "tags": [
        "participle",
        "past"
      ]
    }
  ],
  "head_templates": [
    {
      "args": {
        "1": "be<is,being,was,been> on to"
      },
      "expansion": "be on to (third-person singular simple present is on to, present participle being on to, simple past was on to, past participle been on to)",
      "name": "en-verb"
    }
  ],
  "lang": "English",
  "lang_code": "en",
  "pos": "verb",
  "related": [
    {
      "word": "catch on to"
    },
    {
      "word": "cotton on to"
    }
  ],
  "senses": [
    {
      "categories": [
        "English entries with incorrect language header",
        "English idioms",
        "English lemmas",
        "English multiword terms",
        "English phrasal verbs",
        "English phrasal verbs formed with \"on\"",
        "English phrasal verbs formed with \"to\"",
        "English terms with usage examples",
        "English verbs",
        "Pages with 1 entry",
        "Pages with entries"
      ],
      "examples": [
        {
          "text": "I was planning it as a surprise, but I think he is on to me.",
          "type": "example"
        }
      ],
      "glosses": [
        "To figure out; to realize the truth."
      ],
      "links": [
        [
          "figure",
          "figure"
        ]
      ],
      "raw_glosses": [
        "(idiomatic) To figure out; to realize the truth."
      ],
      "tags": [
        "idiomatic"
      ]
    }
  ],
  "sounds": [
    {
      "audio": "en-au-be on to.ogg",
      "mp3_url": "https://upload.wikimedia.org/wikipedia/commons/transcoded/a/a9/En-au-be_on_to.ogg/En-au-be_on_to.ogg.mp3",
      "ogg_url": "https://upload.wikimedia.org/wikipedia/commons/a/a9/En-au-be_on_to.ogg"
    }
  ],
  "word": "be on to"
}